At this current moment I've been trying to work through an issue I've had with my Hangman JS game. I've spent the last week attempting to replace "underscores", which I have as placeholders for the current secret word. My idea was to loop through the correctLettersOUT, and wherever that particular letter exists in the placeholder would replace it with said letter. This small part of my code below is where the issue is I believe, but I have also created a function in my whole code if a new function necessary.
Any advice is appreciated.
function startGame() {
var testWord = document.getElementById("randTest").innerHTML = secretWord;
var correctLettersOUT = "";
document.getElementById("currentGuess").innerHTML = secretBlanks(secretWord)
function secretBlanks(secretWord) {
for (var i = 0; i < secretWord.length; i++) {
correctLettersOUT += ("_ ");
}
return correctLettersOUT;
}
}
The snippet of my JS is below, it may be large but all of it is necessary. If you wish to view the whole code in it's entirety, the link is CodePen Link.
var guessWords = ["school", "test", "quiz", "pencil", "ruler", "protractor", "teacher", "homework", "science", "math", "english", "history", "language", "elective", "bully", "grades", "recess", ];
var secretWord = guessWords[Math.floor(Math.random() * guessWords.length)];
var wrongLetters = [];
var correctLetters = [];
var repeatLetters = [];
var guesses = Math.round((secretWord.length) + (.5 * secretWord.length));
var correctLettersOUT = "";
function startGame() {
var testWord = document.getElementById("randTest").innerHTML = secretWord;
var correctLettersOUT = "";
document.getElementById("currentGuess").innerHTML = secretBlanks(secretWord)
function secretBlanks(secretWord) {
for (var i = 0; i < secretWord.length; i++) {
correctLettersOUT += ("_ ");
}
return correctLettersOUT;
}
}
function correctWord() {
var guessLetter = document.getElementById("guessLetter").value;
document.getElementById("letter").innerHTML = guessLetter;
for (var i = 0; i < secretWord.length; i++) {
if (correctLetters.indexOf(guessLetter) === -1)
{
if (guessLetter === secretWord[i]) {
console.log(guessLetter === secretWord[i]);
correctLettersOUT[i] = guessLetter;
correctLetters.push(guessLetter);
break;
}}
}
if (wrongLetters.indexOf(guessLetter) === -1 && correctLetters.indexOf(guessLetter) === -1) {
wrongLetters.push(guessLetter);
}
console.log(correctLetters); //Used to see if the letters were added to the correct array**
console.log(wrongLetters);
wordGuess();
}
function wordGuess() {
if (guessLetter.value === '') {
alert("You didn't guess anything.");
} else if (guesses > 1) {
// Counts down.
guesses--;
console.log('Guesses Left: ' + guesses);
// Resets the input to a blank value.
let guessLetter = document.getElementById('guessLetter');
guessLetter.value = '';
} else {
console.log('Game Over');
}
//console.log(guesses)
}
function replWord() { }
One solution to see if the word has been guessed completely and create the partially guessed display with the same info, is to keep a Set with the not yet guessed letters, initialized at game start unGuessed = new Set(secretWord);
Since the Set's delete method returns true if the letter was actually removed (and thus existed), it can be used as a check if a correct letter was entered.
Subsequently, the display can be altered in a single place (on startup and after guessing), by mapping the letters of the word and checking if the letter is already guessed:
function alterDisplay(){
document.getElementById("currentGuess").innerHTML =
[...secretWord].map(c=>unGuessed.has(c) ? '_' : c).join(' ');
}
Some mockup code:
let guessWords = ["school", "test", "quiz", "pencil", "ruler", "protractor", "teacher", "homework", "science", "math", "english", "history", "language", "elective", "bully", "grades", "recess", ],
secretWord, unGuessed, guesses;
function startGame() {
secretWord = guessWords[Math.floor(Math.random() * guessWords.length)];
guesses = Math.round(1.5 * secretWord.length);
unGuessed = new Set(secretWord);
setStatus('');
alterDisplay();
}
function alterDisplay(){
document.getElementById("currentGuess").innerHTML = [...secretWord].map(c=>unGuessed.has(c) ? '_' : c).join(' ');
}
function setStatus(txt){
document.getElementById("status").innerHTML = txt;
}
function correctWord() {
let c= guessLetter.value[0];
guessLetter.value = '';
if (!c) {
setStatus("You didn't guess anything.");
}
else if(unGuessed.delete(c)){
alterDisplay();
if(!unGuessed.size) //if there are no unguessed letters left: the word is complete
setStatus('Yep, you guessed it');
}
else if(--guesses < 1){
setStatus('Game Over!');
}
else
setStatus('Guesses Left: ' + guesses);
}
startGame();
let gl = document.getElementById("guessLetter");
gl.onkeyup= correctWord; //for testing: bind to keyup
gl.value = secretWord[1];correctWord(); //for testing: try the 2nd letter on startup
<div id=currentGuess></div>
<input id=guessLetter><span id=letter></span>
<div id='status'></div>
I am trying to expand an algebraic term.
(x+1)(x+1)/x => x + 2 + x^-1
(x+1)^3 => x^3 + 3x^2 + 3x + 1
(x^2*x)(x^2) => x^5
This is my attempt at it. I have tried a lot of ways trying to fix the problems below.
Problems:
Like terms should be added together
(x+1)(x+1)(x+1) should be valid.
(x+1)^2 should be equal to (x+1)(x+1)
x(x+1) should be valid
1x^n should just be x^n
There should be no 0x^n terms.
nx^0 terms should just be n
Code Snippet:
function split(input) {
return ((((input.split(")(")).toString()).replace(/\)/g, "")).replace(/\(/g, "")).split(','); }
function strVali(str) {
str = str.replace(/\s+/g, "");
var parts = str.match(/[+\-]?[^+\-]+/g);
// accumulate the results
return parts.reduce(function(res, part) {
var coef = parseFloat(part) || +(part[0] + "1") || 1;
var x = part.indexOf('x');
var power = x === -1 ?
0:
part[x + 1] === "^" ?
+part.slice(x + 2) :
1;
res[power] = (res[power] || 0) + coef;
return res;
}, {});
}
function getCoeff(coeff) {
var powers = Object.keys(strVali(coeff));
var max = Math.max.apply(null, powers);
var result = [];
for(var i = max; i >= 0; i--)
result.push(strVali(coeff)[i] || 0);
return result; }
function evaluate(expression) {
var term1 = getCoeff(expression[0]);
var term2 = getCoeff(expression[1]);
var expand = "";
for ( var j = 0; j < term1.length; j++ ) {
for ( var i = 0; i < term2.length; i++ ) {
expand += Number(term1[j] * term2[i]) + 'x^ ' + (Number(term1.length) - 1 - j + Number(term2.length) - 1 - i) + ' + ';
}}
var final = "";
for ( var Z = 0; Z < getCoeff(expand).length; Z++) {
final += ' ' + getCoeff(expand)[Z] + 'x^ {' + (getCoeff(expand).length - Z - 1) + '} +';
}
final = "$$" + ((((((final.replace(/\+[^\d]0x\^ \{[\d]+\}/g,'')).replace(/x\^ \{0}/g,'')).replace(/x\^ \{1}/g,'x')).replace(/[^\d]1x\^ /g,'+ x^')).replace(/\+ -/g,' - ')).slice(0, -1)).substring(1,(final.length)) + "$$";
document.getElementById('result').innerHTML = final;
MathJax.Hub.Queue(["Typeset", MathJax.Hub, document.getElementById('result')]);
}
function caller() {
var input = document.getElementById('input').value;
evaluate(split(input)); }
div.wrapper {
width: 100%;
height:100%;
border:0px solid black;
}
input[type="text"] {
display: block;
margin : 0 auto;
padding: 10px;
font-size:20px;
}
button{
margin:auto;
display:block;
background-color: white;
color: black;
border: 2px solid #555555;
padding-left: 20px;
padding-right: 20px;
font-size: 20px;
margin-top:10px;
}
button:hover {
box-shadow: 0 12px 16px 0 rgba(0,0,0,0.24),0 17px 50px 0 rgba(0,0,0,0.19);
}
<script type="text/javascript" async
src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-MML-AM_CHTML">
</script>
<div class='wrapper'><input id="input" title="Enter Expression" type="text" value="(x^2+x+1)(x^2+x+1)"></div>
<div> <button onclick="caller()">Click</button></div>
<div id="result">$$x^4 + 2x^3 + 3x^2 + 2x + 1$$</div>
Reference:
How to calculate coefficients of polynomial expansion in javascript
Getting coefficients of algebraic term
How to get a term before a character?
Edit: I have re-written my original answer from when the question did not include the - and / operators). My new answer supports - and /.
Since you have not defined a precise grammar, I have made some assumptions. I support the +, -, /, ^ operators and the implicit multiply. These can operate on numbers, x and (...) expressions, except that right hand side of the ^ operator must be a number. I allow spaces between tokens.
Limitations: The -is a binary not unary - operator, So x-2 if OK, -2 on its own is a syntax error. The / is limited. You may divide by a value with a single coefficient such as 2, 'x', 2x^2, but not by cannot have 1/(x^2+1), which would evaluate to an infinite series.
It first takes the string and wraps it in a 'tokenizer' which lets you look it one token at a time, where a token is a number, x, ( ) or operator.
It then calls evaluateSum() which evaluates things separated by + or -, where each thing is a product evaluated by evaluateProduct(). This in turn uses evaluatePower() to evalue the ^. Finally evaluateTerm() looks for x, numbers and bracketed sub-expressions which are evaluates recursively with evaluateSum(). This hierarchy creates the correct operator precedence and evaluation order.
Each layer of the evaluation returns a 'coefficients' object which s array-like, but may contain megative indexes. For example [1,0,1] means 1+x^2.
It can cope with any number of nested brackets and a lot of other case such as xx(x) is x^3, 2^3 is 8. I have added a few throws for syntax errors, for example 2^x is illegal.
function makeTokenizer(source) {
var c, i, tokenizer;
i = 0; // The index of the current character.
c = source.charAt(i); // The current character.
function consumeChar() { // Move to next c, return previous c.
var prevC = c;
i += 1;
c = source.charAt(i);
return prevC;
}
tokenizer = {
next : function () {
var str;
while (c === ' ') { // Skip spaces
consumeChar();
}
if (!c) {
tokenizer.token = undefined; // End of source
} else if (c >= '0' && c <= '9') { // number
str = consumeChar(); // First digit
while (c >= '0' && c <= '9') { // Look for more digits.
str += consumeChar();
}
tokenizer.token = Number(str);
} else if (c === "x") {
tokenizer.token = consumeChar();
} else { // single-character operator
tokenizer.token = consumeChar();
}
}
};
tokenizer.next(); // Load first token.
return tokenizer;
}
function makeCoefficients() { // Make like an array but can have -ve indexes
var min = 0, max = 0, c = {};
return {
get: function (i) {
return c[i] || 0;
},
set: function (i, value) {
c[i] = value;
min = Math.min(i, min);
max = Math.max(i + 1, max);
return this; // for chaining
},
forEach: function (callback) {
var i;
for (i = min; i < max; i += 1) {
if (this.get(i)) {
callback(this.get(i), i);
}
}
},
toString: function () {
var result = "", first = true;
this.forEach(function (val, power) {
result += (val < 0 || first) ? "" : "+";
first = false;
result += (val === 1 && power !== 0) ? "" : val;
if (power) {
result += "x";
if (power !== 1) {
result += "^" + power;
}
}
});
return result;
},
toPowerOf: function (power) {
if (power === 0) {
return makeCoefficients().set(0, 1); // Anything ^0 = 1
}
if (power === 1) {
return this;
}
if (power < 0) {
throw "cannot raise to negative powers";
}
return this.multiply(this.toPowerOf(power - 1));
},
multiply: function (coefficients) {
var result = makeCoefficients();
this.forEach(function (a, i) {
coefficients.forEach(function (b, j) {
result.set(i + j, result.get(i + j) + a * b);
});
});
return result;
},
divide: function (coefficients) {
// Division is hard, for example we cannot do infinite series like:
// 1/(1 + x^2) = sum_(n=0 to infinity) 1/2 x^n ((-i)^n + i^n)
// So we do a few easy cases only.
var that = this, result = makeCoefficients(), done;
coefficients.forEach(function (value, pow) {
that.forEach(function (value2, pow2) {
result.set(pow2 - pow, value2 / value);
});
if (done) {
throw "cannot divide by " + coefficients.toString();
}
done = true;
});
return result;
},
add: function (coefficients, op) {
var result = makeCoefficients();
this.forEach(function (value, i) {
result.set(value, i);
});
op = (op === "-" ? -1 : 1);
coefficients.forEach(function (value, i) {
result.set(i, result.get(i) + value * op);
});
return result;
}
};
}
var evaluateSum; // Called recursively
function evaluateTerm(tokenizer) {
var result;
if (tokenizer.token === "(") {
tokenizer.next();
result = evaluateSum(tokenizer);
if (tokenizer.token !== ")") {
throw ") missing";
}
tokenizer.next();
} else if (typeof tokenizer.token === "number") {
result = makeCoefficients().set(0, tokenizer.token);
tokenizer.next();
} else if (tokenizer.token === "x") {
tokenizer.next();
result = makeCoefficients().set(1, 1); // x^1
} else {
return false; // Not a 'term'
}
return result;
}
function evaluatePower(tokenizer) {
var result;
result = evaluateTerm(tokenizer);
if (tokenizer.token === "^") {
tokenizer.next();
if (typeof tokenizer.token !== "number") {
throw "number expected after ^";
}
result = result.toPowerOf(tokenizer.token);
tokenizer.next();
}
return result;
}
function evaluateProduct(tokenizer) {
var result, term, divOp;
result = evaluatePower(tokenizer);
if (!result) {
throw "Term not found";
}
while (true) {
divOp = (tokenizer.token === "/");
if (divOp) {
tokenizer.next();
term = evaluatePower(tokenizer);
result = result.divide(term);
} else {
term = evaluatePower(tokenizer);
if (!term) {
break;
}
result = result.multiply(term);
}
}
return result;
}
function evaluateSum(tokenizer) {
var result, op;
result = evaluateProduct(tokenizer);
while (tokenizer.token === "+" || tokenizer.token === "-") {
op = tokenizer.token;
tokenizer.next();
result = result.add(evaluateProduct(tokenizer), op);
}
return result;
}
function evaluate(source) {
var tokenizer = makeTokenizer(source),
coefficients = evaluateSum(tokenizer);
if (tokenizer.token) {
throw "Unexpected token " + tokenizer.token;
}
console.log(source + " => " + coefficients.toString());
}
// Examples:
evaluate("(x+1)(x+1)"); // => 1+2x+x^2
evaluate("(x+1)^2"); // => 1+2x+x^2
evaluate("(x+1)(x+1)(x+1)"); // => 1+3x+3x^2+x^3
evaluate("(x+1)^3"); // => 1+3x+3x^2+x^3
evaluate("(x)(x+1)"); // => x+x^2
evaluate("(x+1)(x)"); // => x+x^2
evaluate("3x^0"); // => 3
evaluate("2^3"); // => 8
evaluate("(x+2x(x+2(x+1)x))"); // => x+6x^2+4x^3
evaluate("(x+1)(x-1)"); // => -1+x^2
evaluate("(x+1)(x+1)/x"); // x^-1+2+x
//evaluate("(x+1)/(x^2 + 1)"); //throws cannot divide by 1+2x
It can handle +, -, / and implicit multiplication. It expands the parenthesis accordingly and adds them to the original expression while removing the parenthesised version. It collects like terms accordingly. Limitations: It cannot divide by a polynomial and it does not support the * operator.
function strVali(str) {
str = str.replace(/\s+/g, "");
var parts = str.match(/[+\-]?[^+\-]+/g);
return parts.reduce(function(res, part) {
var coef = parseFloat(part) || +(part[0] + "1") || 1;
var x = part.indexOf('x');
var power = x === -1 ?
0:
part[x + 1] === "^" ?
+part.slice(x + 2) :
1;
res[power] = (res[power] || 0) + coef;
return res;
}, {});
}
function getCoeff(coeff) {
var powers = Object.keys(strVali(coeff));
var max = Math.max.apply(null, powers);
var result = [];
for(var i = max; i >= 0; i--)
result.push(strVali(coeff)[i] || 0);
return result; }
function format(str) {
str = ' ' + str;
str = str.replace(/-/g,'+-').replace(/x(?!\^)/g,'x^1').replace(/([+\/*)(])(\d+)([+\/*)(])/g,'$1$2x^0$3').replace(/([^\d])(x\^-?\d+)/g,'$11$2').replace(/(-?\d+x\^\d+)(?=\()/g,'($1)').replace(/(\))(-?\d+x\^\d+)/g,'$1($2)').replace(/([^\)\/])(\()([^\*\/\(\)]+?)(\))(?![(^\/])/g,'$1$3');
str = str.replace(/(\([^\(\)]+?\))\/(\d+x\^-?\d+)/g,'$1/($2)').replace(/(\d+x\^-?\d+)\/(\d+x\^-?\d+)/g,'($1)/($2)').replace(/(\d+x\^-?\d+)\/(\(\d+x\^-?\d+\))/g,'($1)/$2');
return str;
}
function expBrackets(str) {
var repeats = str.match(/\([^\(\)]+?\)\^\d+/g);
if ( repeats === null ) { return str; } else { var totalRepeat = '';
for ( var t = 0; t < repeats.length; t++ ) { var repeat = repeats[t].match(/\d+$/); for ( var u = 0; u < Number(repeat); u++ ) { totalRepeat += repeats[t].replace(/\^\d+$/,''); }
str = str.replace(/\([^\(\)]+?\)\^\d+/, totalRepeat); totalRepeat = ''; }
return str; }
}
function multiply(str) {
var pairs = str.match(/\([^\(\)]+?\)\([^\(\)]+?\)/g);
if ( pairs !== null ) { while ( pairs !== null ) { var output = '';
for (var i = 0; i < pairs.length; i++) { var pair = pairs[i].slice(1).slice(0, -1).split(')('); var firstCoeff = getCoeff(pair[0]); var secondCoeff = getCoeff(pair[1]);
for (var j = 0; j < firstCoeff.length; j++) {
for (var k = 0; k < secondCoeff.length; k++) { output += firstCoeff[j] * secondCoeff[k] + 'x^' + Number(firstCoeff.length - 1 - j + secondCoeff.length - 1 - k) + '+'; } }
var regexp = new RegExp(pairs[i].replace(/\(/g,'\\(').replace(/\+/g,'\\+').replace(/\)/g,'\\)').replace(/\^/g,'\\^').replace(/\-/g,'\\-'));
str = str.replace(regexp, '(' + (output.slice(0, -1).replace(/[^\d]0x\^\d+/g,'')) + ')');
output = ''; }
pairs = str.match(/\([^\(\)]+?\)\([^\(\)]+?\)/g); } }
else { }
str = str.replace(/\+/g,' + ');
return str;
}
function divide(str) {
if ( str.match(/\/(\(-?\d+x\^-?\d+.+?\))/g) === null && str.match(/\//g) !== null ) {
while ( pairs !== null ) {
var pairs = str.match(/\([^\(\)]+?\)\/\([^\(\)]+?\)/g);
var output = '';
for (var i = 0; i < pairs.length; i++) {
var pair = pairs[i].slice(1).slice(0, -1).split(')/(');
var firstCoeff = getCoeff(pair[0]);
var secondCoeff = getCoeff(pair[1]);
for (var j = 0; j < firstCoeff.length; j++) {
for (var k = 0; k < secondCoeff.length; k++) {
output += firstCoeff[j] / secondCoeff[k] + 'x^' + Number(firstCoeff.length - 1 - j - secondCoeff.length + 1 + k) + '+';
output = output.replace(/([+-])Infinityx\^\-?\d+/g,'').replace(/([+-])NaNx\^\-?\d+/g,'');
} }
var regexp = new RegExp(pairs[i].replace(/\(/g,'\\(').replace(/\+/g,'\\+').replace(/\)/g,'\\)').replace(/\^/g,'\\^').replace(/\-/g,'\\-'));
str = str.replace(regexp, '(' + (output.slice(0, -1).replace(/[^\d]0x\^-?\d+/g,'')) + ')');
output = ''; }
pairs = str.match(/\([^\(\)]+?\)\/\([^\(\)]+?\)/g); } }
else { }
return str;
}
function evaluate(str) {
var result = format(divide(format(multiply(expBrackets(format((str)))))));
var resultCollect = '';
result = result.replace(/\s+/g, "").replace(/[^\d]0x\^-?\d+/g,'').replace(/\+/g,' + ');
if ( result === '') {
document.getElementById('result').innerHTML = '$$' + str + '$$' + '$$ = 0 $$';
MathJax.Hub.Queue(["Typeset", MathJax.Hub, document.getElementById('result')]);
} else if ( result.match(/-?\d+x\^-\d+/g) === null && str.match(/\/(\(-?\d+x\^-?\d+.+?\))/g) === null) {
for ( var i = 0; i < getCoeff(result).length; i++ ) {
resultCollect += getCoeff(result)[i] + 'x^' + Number(getCoeff(result).length - 1 - i) + '+' ; }
if ( resultCollect !== '')
resultCollect = '$$ = ' + resultCollect.slice(0,-1).replace(/[^\d]0x\^-?\d+/g,'').replace(/\+/g,' + ').replace(/x\^0/g,'').replace(/x\^1(?!\d+)/g,'x').replace(/\^(-?\d+)/g,'\^\{$1\}').replace(/\+ -/g,' - ') + '$$';
else
resultCollect = 'Error: Trying to divide by a polynomial ';
document.getElementById('result').innerHTML = '$$' + str.replace(/\^(-?\d+)/g,'\^\{$1\}') + '$$' + resultCollect;
MathJax.Hub.Queue(["Typeset", MathJax.Hub, document.getElementById('result')]);
} else {
resultCollect = '$$ = ' + result.replace(/\^(-?\d+)/g,'\^\{$1\}') + '$$';
document.getElementById('result').innerHTML = '$$' + str.replace(/\^(-?\d+)/g,'\^\{$1\}').replace(/\+ -/g,' - ') + '$$' + resultCollect;
MathJax.Hub.Queue(["Typeset", MathJax.Hub, document.getElementById('result')]);
}
}
function caller() {
var input = document.getElementById('input').value;
evaluate(input);
}
div.wrapper {
width: 100%;
height:100%;
border:0 solid black;
}
input[type="text"] {
display: block;
margin : 0 auto;
padding: 10px;
font-size:20px;
}
button{
margin:auto;
display:block;
background-color: white;
color: black;
border: 2px solid #555555;
padding-left: 20px;
padding-right: 20px;
font-size: 20px;
margin-top:10px;
}
button:hover {
box-shadow: 0 12px 16px 0 rgba(0,0,0,0.24),0 17px 50px 0 rgba(0,0,0,0.19);
}
<script type="text/javascript" async
src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-MML-AM_CHTML">
</script>
<input id="input" type="text" title="Enter Expression: ">
<button onclick="caller()">Click</button>
<div id="result"></div>
<div id="errors"></div>
My approach utilizes two helper classes:
-Term: This stores a coefficient and an object, the keys of which are variables and the values of which are the exponents. It has methods for determining whether terms are the "same" (i.e. whether they have the same variables with the same exponents, thus allowing them to be added), adding terms, and multiplying terms.
-Polynomial: This stores an array of terms. It has methods for adding two polynomials, multiplying two polynomials, and simplifying polynomials (eliminating terms with 0 coefficients and combining like terms).
It has two substantial helper functions:
-findOuterParens - Given a string, this function returns the indices of the first outermost pair of left and right parentheses.
-parseExpressionStr - This function uses a regular expression to split a string into three types of substrings: 1) a number, 2) a symbol (i.e. a variable, like 'x' or 'y'), or 3) an operator (*, -, +, ^, /). It creates Polynomial objects for the first two types and leaves the operators as strings.
The expand function runs the show. It takes in a string and returns a Polynomial object representing the expanded form of the polynomial in the string. It does this as follows:
1) It deals with parentheses by recursion. It uses findOuterParens to find all outermost parenthsized substrings. So for "3x*(x+4)+(2(y+1))*t", for instance, it would find "x+4" and "2(y+1)" as parenthsized substrings. It then passes these to itself for further parsing. For "2(y+1)", it would identify "y+1" as a parenthesized substring, and pass this to itself, for three levels of recursion for this example.
2) It deals with other parts of the string using parseExpressionStr. After steps 1 and 2, it has an array containing Polynomial objects and operators (stored as strings). It then proceeds to simplifying and expanding.
3) It converts subtraction subproblems to addition subproblems by replacing all -'s with +'s and multiplying all polynomials following -'s by -1.
4) It converts division subproblems to multiplication subproblems by replacing /'s with *'s and inverting the Polynomial following the /. If the polynomial following the / has more than one term, it throws an error.
5) It converts power subproblems to multiplication subproblems by replacing ^'s with a series of multiplications.
6) It adds in implicit *'s. I.e. if two Polynomial elements are right next to each other in the array, then it's inferred that they are being multiplied, so, e.g. '2*x' == '2x'.
7) Now the array has polynomial objects alternating with either '+' or '*'. It first performs all polynomial multiplications and then performs all additions.
8) It performs a final simplification step and returns the resulting expanded polynomial.
<html>
<head></head>
<body></body>
<script>
function findOuterParens(str) {
var leftIndex = str.indexOf('('), leftNum = 1, rightNum = 0;
if (leftIndex === -1)
return
for (var i=leftIndex+1; i<str.length; i++) {
if (str[i] === '(')
leftNum++;
else if (str[i] === ')')
rightNum++, rightIndex=i;
if (leftNum === rightNum)
return {start: leftIndex, end: rightIndex}
}
throw Error('Parenthesis at position ' + leftIndex + ' of "' + str + '" is unpaired.');
}
function parseExpressionStr(inputString) {
var result = [], str = inputString;
while (str) {
var nextPart = str.match(/([\d]+)|([\+\-\^\*\/])|([a-zA-z])/);
if (!nextPart)
return result;
if (nextPart.length === 0)
throw Error('Unable to parse expression string "' + inputString + '". Remainder "' + str + '" could not be parsed.');
else if (nextPart[1]) // First group (digits) matched
result.push(new Polynomial(parseFloat(nextPart[0])));
else if (nextPart[3]) // Third group (symbol) matched
result.push(new Polynomial(nextPart[0]));
else // Second group (operator) matched
result.push(nextPart[0]);
str = str.substring(nextPart.index+nextPart[0].length);
}
return result
}
function isOperator(char) {
return char === '*' || char === '/' || char === '^' || char === '+' || char === '-';
}
function Polynomial(value) {
this.terms = (value!==undefined) ? [new Term(value)] : [];
}
Polynomial.prototype.simplify = function() {
for (var i=0; i<this.terms.length-1; i++) {
if (this.terms[i].coeff === 0) {
this.terms.splice(i--, 1);
continue;
}
for (var j=i+1; j<this.terms.length; j++) {
if (Term.same(this.terms[i], this.terms[j])) {
this.terms[i] = Term.add(this.terms[i], this.terms[j]);
this.terms.splice(j--, 1);
}
}
}
}
Polynomial.add = function(a, b) {
var result = new Polynomial();
result.terms = a.terms.concat(b.terms);
result.simplify();
return result
}
Polynomial.multiply = function(a, b) {
var result = new Polynomial();
a.terms.forEach(function(aTerm) {
b.terms.forEach(function (bTerm) {
result.terms.push(Term.multiply(aTerm, bTerm));
});
});
result.simplify();
return result
}
Polynomial.prototype.toHtml = function() {
var html = ''
for (var i=0; i<this.terms.length; i++) {
var term = this.terms[i];
if (i !== 0)
html += (term.coeff < 0) ? ' - ' : ' + ';
else
html += (term.coeff < 0) ? '-' : '';
var coeff = Math.abs(term.coeff);
html += (coeff === 1 && Object.keys(term.symbols).length > 0) ? '' : coeff;
for (var symbol in term.symbols) {
var exp = term.symbols[symbol];
exp = (exp !== 1) ? exp : '';
html += symbol + '<sup>' + exp + '</sup>';
}
}
return html;
}
function Term(value) {
this.symbols = {};
if (typeof value==='string') { // Symbol
this.symbols[value] = 1;
this.coeff = 1;
} else if (typeof value==='number') { // Number
this.coeff = value;
} else {
this.coeff = 1;
}
}
Term.same = function(a, b) {
if (Object.keys(a.symbols).length != Object.keys(b.symbols).length)
return false
else
for (var aSymbol in a.symbols)
if (a.symbols[aSymbol] != b.symbols[aSymbol]) return false
return true
}
Term.add = function(a, b) {
var result = new Term();
Object.assign(result.symbols, a.symbols);
result.coeff = a.coeff + b.coeff;
return result
}
Term.multiply = function(a, b) {
var result = new Term();
Object.assign(result.symbols, a.symbols);
for (var symbol in b.symbols) {
if (!(symbol in result.symbols))
result.symbols[symbol] = 0;
result.symbols[symbol] += b.symbols[symbol];
if (result.symbols[symbol] === 0)
delete result.symbols[symbol];
}
result.coeff = a.coeff * b.coeff;
return result
}
function expand(str) {
var result = [];
var parens = findOuterParens(str);
while (parens) {
result = result.concat(parseExpressionStr(str.slice(0,parens.start)));
result.push(expand(str.slice(parens.start+1, parens.end)))
str = str.slice(parens.end+1);
parens = findOuterParens(str);
}
result = result.concat(parseExpressionStr(str));
// Move -s to coefficients
var minus = result.indexOf('-'), minusPoly = new Polynomial(-1);
while (minus !== -1) {
result[minus] = '+';
result[minus+1] = Polynomial.multiply(minusPoly, result[minus+1]);
minus = result.indexOf('-');
}
// Get rid of +s that follow another operator
var plus = result.indexOf('+');
while (plus !== -1) {
if (plus===0 || isOperator(result[plus-1])) {
result.splice(plus--, 1);
}
plus = result.indexOf('+', plus+1);
}
// Convert /s to *s
var divide = result.indexOf('/');
while (divide !== -1) {
result[divide] = '*';
var termsToInvert = result[divide+1].terms;
if (termsToInvert.length > 1)
throw Error('Attempt to divide by a polynomial with more than one term.');
var termToInvert = termsToInvert[0];
for (var symbol in termToInvert.symbols) {
termToInvert.symbols[symbol] = -termToInvert.symbols[symbol];
}
termToInvert.coeff = 1/termToInvert.coeff;
divide = result.indexOf('/');
}
// Convert ^s to *s
var power = result.indexOf('^');
while (power !== -1) {
var exp = result[power+1];
if (exp.terms.length > 1 || Object.keys(exp.terms[0].symbols).length != 0)
throw Error('Attempt to use non-number as an exponent');
exp = exp.terms[0].coeff;
var base = result[power-1];
var expanded = [power-1, 3, base];
for (var i=0; i<exp-1; i++) {
expanded.push('*');
expanded.push(base);
}
result.splice.apply(result, expanded);
power = result.indexOf('^');
}
// Add implicit *s
for (var i=0; i<result.length-1; i++)
if (!isOperator(result[i]) && !(isOperator(result[i+1])))
result.splice(i+1, 0, '*');
// Multiply
var mult = result.indexOf('*');
while (mult !== -1) {
var product = Polynomial.multiply(result[mult-1], result[mult+1]);
result.splice(mult-1, 3, product);
mult = result.indexOf('*');
}
// Add
var add = result.indexOf('+');
while (add !== -1) {
var sum = Polynomial.add(result[add-1], result[add+1]);
result.splice(add-1, 3, sum);
add = result.indexOf('+');
}
result[0].simplify();
return result[0];
}
var problems = ['(x+1)(x+1)/x', '(x+1)^3', '(x^2*x)(x^2)', '(x+1)(x+1)(x+1)',
'(x+1)^2', 'x(x+1)', '1x^4', '(x + (x+2))(x+5)', '3x^0', '2^3',
'(x+2x(x+2(x+1)x))', '(x+1)(x-1)', '(x+1)(y+1)', '(x+y+t)(q+x+7)'];
var solutionHTML = '';
for (var i = 0; i<problems.length; i++) {
solutionHTML += problems[i] + ' => ' + expand(problems[i]).toHtml() + '<br>';
}
document.body.innerHTML = solutionHTML;
</script>
</html>
It outputs:
I been doing this javascript challenge and I'm pretty close, but something is off.Here's the challenge:
Given an array of strings containing three types of braces: round (), square [] and curly {}
Your task is to write a function that checks whether the braces in each string are correctly matched. Prints 1 to standard output (console.log) if the braces in each string are matched and 0 if they're not (one result per line)
my code is this:
var infoToParse = [ ")(){}", "[]({})", "([])", "{()[]}", "([)]" ];
function checkBraces(infoToParse) {
var tabChars = infoToParse;
for (i= 0; tabChars.length - 1; i+=1) {
if (tabChars[i].charAt(0) === tabChars[i].charAt(tabChars[i].length-1)){
console.log(1);
}else{
console.log(0);
}
}
}
checkBraces(infoToParse);
The output with the current array items should be Output:
0
1
1
1
0
As pointed out in the comment, only having the first and the last character same would not result in a correct solution.
You can try the following technique:
Maintain a stack, each time you encounter an opening bracket i.e round "(", square "[" or curly "{"; push this into stack. Now whenever you encounter a closing bracket, pop an element from the stack. If these two match i.e both are of same type, then carry on till stack and string both are empty. If at any point these don't match then break and return false.
I'll write a code for it and post it soon.
I guess you could do it in this way, keeping a "tree" of starting positions. Didn't test any other testcases than your own though :)
var testCases = [")(){}", "[]({})", "([])", "{()[]}", "([)]"];
var braceType = {
round: ["(", ")"],
curly: ["{", "}"],
square: ["[", "]"]
};
var bracePosition = {
start: ["{", "(", "["],
end: ["}", ")", "]"]
};
function typeOfBraces(sign) {
for (var property in braceType) {
if (braceType[property].indexOf(sign) < 0) {
continue;
}
if (bracePosition.start.indexOf(sign) < 0) {
return {
type: property,
position: "end"
};
} else {
return {
type: property,
position: "start"
};
}
}
throw "Sign is not a brace!";
};
function Braces(brace, parent, type) {
this.brace = brace;
this.parent = parent || null;
this.type = type || {
type: 'init',
position: ''
};
this.children = [];
this.nextBrace = function(nextSign) {
var nextType = typeOfBraces(nextSign);
if (nextType.position === 'start') {
var child = new Braces(nextSign, this, nextType);
this.children.push(child);
return child;
}
if (nextType.position === 'end') {
if (this.type.position === '') {
throw 'Cannot start with an end tag!';
}
if (this.type.position === 'end' && this.parent === null) {
throw 'Cannot end the sequence';
}
if (this.type.position === 'end' && this.parent.position === 'start') {
if (this.type.type === this.parent.type) {
var child = new Braces(nextSign, this.parent, nextType);
this.parent.children.add(child);
return this.parent;
}
}
}
if (this.type.position === 'start' && nextType.type === this.type.type && nextType.position === 'end') {
return this.parent;
}
return new Braces(nextSign, this, nextType);
};
}
for (var i = 0; i < testCases.length; i++) {
var brace = new Braces(testCases[i]);
for (var j = 0, len = testCases[i].length; j < len; j++) {
try {
brace = brace.nextBrace(testCases[i][j]);
} catch (e) {
console.log(e);
brace = null;
break;
}
}
if (brace != null && brace.parent == null) {
// valid entry
console.log(brace);
console.log(testCases[i] + " is a valid sequence");
} else {
// invalid entry
console.log(testCases[i] + " is an invalid sequence");
}
}
or, to make it a bit easier and to check check the brackets:
function validBraces(braceSequence) {
var stack = '',
i, len, lastStack = -1,
toAdd = "{([",
toRemove = "})]",
sign;
for (i = 0, len = braceSequence.length; i < len; i++) {
sign = braceSequence[i];
if (toAdd.indexOf(sign) >= 0) {
stack += sign;
lastStack++;
} else if (toRemove.indexOf(sign) >= 0) {
if (toAdd.indexOf(stack.charAt(lastStack)) !== toRemove.indexOf(sign)) {
// format exception
console.warn('Format exception, didn\'t expect ' + sign + ' (current stack: ' + stack + ')');
return false;
} else {
stack = stack.slice(0, -1);
lastStack--;
}
} else {
console.warn('Invalid character exception, didn\'t expect ' + sign + ' (current stack: ' + stack + ')');
return false;
}
}
return true;
}
var testCases = [")(){}", "[]({})", "([])", "{()[]}", "([)]"];
for (var i = 0; i < testCases.length; i++) {
if (validBraces(testCases[i])) {
console.log(testCases[i] + ' is a valid sequence');
} else {
console.log(testCases[i] + ' is an invalid sequence');
}
}
If you can use Regular Expressions, you can really slim it down:
var stringArray = [ ")(){}", "[]({})", "([])", "{()[]}", "([)]" ];
function checkBraces(infoToParse) {
for (i = 0; i < infoToParse.length; i += 1) {
var regX = /^\[.*\]$|^\{.*\}$|^\(.*\)$/gi;
var str = infoToParse[i];
console.log(str.match(regX) ? 1 : 0);
}
}
checkBraces(stringArray);
Also, as I stated in my comment, your for syntax was off. Oh, and instead of i+=1, you can use i++ to simplify it.
I'm trying to write a simple javascript program to check if a letter is a vowel. The problem is the output is incorrect and should say that " a is a vowel."
Javascript:
function findvowel(letter1, vowels) {
var count = vowels.length;
for (var i = 0; i < count; i++) {
if (vowels[i] === letter1) {
var message1 = " is a vowel";
document.getElementById('exercise3').innerHTML = letter1 + message1;
} else {
var message2 = " is a consonant";
document.getElementById('exercise3').innerHTML = letter1 + message2;
}
}
}
HTML:
<script>
$(document).ready(function() {
findvowel("a",["a","e","i","o","u"]);
});
</script>
Output:
a is a consonant
Add break to your loop so it doesn't keep going.
function findvowel(letter1, vowels) {
var count = vowels.length;
for (var i = 0; i < count; i++) {
if (vowels[i] === letter1) {
var message1 = " is a vowel";
document.getElementById('exercise3').innerHTML = letter1 + message1;
break;
} else {
var message2 = " is a consonant";
document.getElementById('exercise3').innerHTML = letter1 + message2;
}
}
}
You can actually use return false; to stop your function right away when a vowel is matched, however in normal cases break will be used because there might be other codes going on after the loop.
BTW:
function findvowel(letter){
//thanks p.s.w.g for reminding me []
return letter+" is a "+(/[aeiou]/i.test(letter)?"vowel":"constant");
}
You're testing the vowel in the for-loop and updating the output every time. So the output will only display if the last vowel that was tested matched the input. Instead, you should break out of the for-loop if a vowel is found, and only display a failure (" is a consonant") after you've tested all the vowels and you weren't able to find a match:
var count = vowels.length;
for (var i = 0; i < count; i++) {
if (vowels[i] === letter1) {
var message1 = " is a vowel";
document.getElementById('exercise3').innerHTML = letter1 + message1;
return;
}
}
var message2 = " is a consonant";
document.getElementById('exercise3').innerHTML = letter1 + message2;
But this method could be simplified to:
function findvowel(letter1) {
var isVowel = "aeiou".indexOf(letter1) > -1;
var message = letter1 + " is a " + (isVowel ? "vowel" : "consonant");
document.getElementById('exercise3').innerHTML = message;
}
This is what I would do, using native functions:
var letter = "a";
var isVowel = ["a","e","i","o","u"].some(function(vowel){
return vowel === letter;
});
Rergarding your message, I would try something like:
var message = letter + (isVowel ? " is a vowel" : " is a consonant");
I would pass in an object instead of an array and take advantage of the constant time lookup using the 'in' keyword. No need for a loop.
function findvowel(letter1, vowels) {
if (letter1 in vowels) {
var message1 = " is a vowel";
document.getElementById('exercise3').innerHTML = letter1 + message1;
} else {
var message2 = " is a consonant";
document.getElementById('exercise3').innerHTML = letter1 + message2;
}
}
then
var obj = {'a': true, 'e': true, 'i': true, 'o': true, 'u': true}
then call it
findvowel('a', obj)
Since you're already using jQuery, which offers $.inArray(), why don't you do this?
var vowels = ["a", "e", "i", "o", "u"];
$(document).ready(function() {
var letter = 'u';
var found = $.inArray(letter, vowels) > -1;
if(found) {
console.log(letter + ' is a vowel');
} else {
console.log(letter + ' is a consonant');
}
});