Develop Reference

Caesar Cipher technique and reverse case in javascript

I am beginner and want to make my own function.
I want to hash the password by shifting every character by given x
positions and reverse to lowercase/uppercase.
I think the code below should return "EFGH7654" but it return 55 with no error message.
How can I fix it? Is it because of I put a function in a function?
Or I type wrong any thing?
function hashPassword(password, x) {
// password is a string, x is a number
// return a string
// (ex. password = 'ab1By', x = 3 so it should return "DE4eB")
function shift(text, s) {
result = "";
for (let i = 0; i < text.length; i++) {
let char = text[i];
if (char.toUpperCase(text[i])) {
let ch = String.fromCharCode((char.charCodeAt(0) + s - 65) % 26 + 65);
result += ch;
} else {
let ch = String.fromCharCode((char.charCodeAt(0) + s - 97) % 26 + 97);
result += ch;
}
}
return result;
}
function reversecase(x) {
var output = '';
for (var i = 0, len = x.length; i < len; i++) {
var character = x[i];
if (character == character.toLowerCase()) {
// The character is lowercase
output = output + character.toUpperCase();
} else {
// The character is uppercase
output = output + character.toLowerCase();
}
}
return output
}
var str = "";
var result = "";
var charcode = "";
for (var i = 0; i < password.length; i++) {
if (typeof password[i] === typeof str) {
char = shift(password[i], x)
charcode = reversecase(char)
result += charcode;
} else {
num = password[i] + x
number = num % 10
result += number.toString()
}
}
return result
};
console.log(hashPassword("abcd4321", 4))

There a quite some problems in your code.
The first problem here is not only the nesting, but the fact that you're defining the result variable in the outer function scope using the var keyword. Then you use (read/write) that variable in different places.
In function shift() (also in return statement)
In the outer function (also in return statement)
The thing you have to understand is, that you're referring to the same variable result every time. To ensure that your variables are scoped, i.e. are only valid within a block (if statement, function body, etc.), you should use the let or const keywords. This makes your code a lot safer.
The second problem are some assumptions you make regarding data types. If you have a string let s = "my string 123", the expression typeof s[x] === 'string' will be true for every x in s.
Another problem is the algorithm itself. The outer function hashPassword() iterates over all characters of the input string. Within that loop you call function shift(password[i], x), passing a single character. The first parameter of shift() is called text - and there is another for loop (which is confusing and does not make sense).
To make things short, please have a look at this simplified version:
function shift(char, x) {
let result;
const code = char.charCodeAt(0);
if (code >= 65 && code < 91) {
result = String.fromCharCode((code + x - 65) % 26 + 65);
}
else if (code >= 48 && code <= 57) {
result = String.fromCharCode((code + x - 48) % 10 + 48);
}
else {
result = String.fromCharCode((code + x - 97) % 26 + 97);
}
return result;
}
function reverseCase(character) {
if (character === character.toLowerCase()) {
return character.toUpperCase();
}
else {
return character.toLowerCase();
}
}
function hashPassword(password, x) {
let result = "";
for (let i = 0; i < password.length; i++) {
const char = shift(password[i], x);
result += reverseCase(char);
}
return result;
}
console.log(hashPassword("abcd4321", 4)); // Output: EFGH8765

Why can I not set the value of a variable outside a JavaScript while loop?

I'm trying to work through a binary challenge and it requires setting a midway point between the start and end of an array.
This is the code:
function binary (val, nums) {
var start = nums[0];
var end = nums.length -1;
var found = false;
var mid = Math.floor((start + end)/2);
var position = -1;
while(!found && start <= end) {
if (nums[mid] === val) {
found = true;
position = mid;
}
else if (nums[mid] > val) {
end = mid -1;
}
else {
start = mid + 1;
}
}
return position;
}
console.log(binarySearch(12, [1,2,3,4,5,6,7,12]))
The console returns nothing but the function doesn't stop either. However, if I declare var mid outside the loop and then set the value within the loop like so
var mid;
while(!found && start <= end) {
mid = Math.floor((start+end)/2)
if (nums[mid] === val) {
found = true;
position = mid;
}
else if (nums[mid] > val) {
end = mid -1;
}
else {
start = mid + 1;
}
}
It returns the correct value. Why is this?

In the first code snippet (outside while loop), you are never changing mid value where as in second code snippet, you are updating mid in each iteration based on start and end values and hence the difference in result.

all valid combinations of n-pair of parenthesis

I am learning js now..
I am trying to write a simple js programme..
what I am trying to do is to print all valid combinations of n-pair
of parenthesis(properly opened and closed)
eg (), (()()),(())
i have written the logic can you tell me whether its correct or not
https://jsfiddle.net/e7mcp6xb/
module.exports = Parentheses = (function() {
var _isParenthesesMatch = function(str) {
var parentheses = str.length;
var rightParentheses = '(';
var leftParentheses = ')';
var rightCount = 0;
var leftCount = 0;
for(i=0;i<=str.length;i++){
if(rightParentheses == str.charAt(i))
{
rightCount++;
}
else if(leftParentheses == str.charAt(i))
{
leftCount++;
}
}
if(rightCount == leftCount){
return true;
}
else(rightCount != leftCount){
return false;
}
}
}());

The check is wrong, but You can fix it easily: In each step of the for loop the number of opening parenthesis cannot be smaller than the number of closing ones:
if (rightCount < leftCount)
return false;
The whole function should look like this:
function(str) {
var rightParentheses = '(';
var leftParentheses = ')';
var rightCount = 0;
var leftCount = 0;
for (var i = 0; i <= str.length; i++) {
if (rightParentheses == str.charAt(i))
rightCount++;
else if (leftParentheses == str.charAt(i))
leftCount++;
if (rightCount < leftCount)
return false;
}
return rightCount == leftCount;
}
If You'd like to generate all valid strings, you can use this function:
function nPair(n) {
if (n == 0)
return [""];
var result = [];
for (var i = 0; i < n; ++i) {
var lefts = nPair(i);
var rights = nPair(n - i - 1);
for (var l = 0; l < lefts.length; ++l)
for (var r = 0; r < rights.length; ++r)
result.push("(" + lefts[l] + ")" + rights[r]);
}
return result;
}
// result of nPair(3):
// ["()()()", "()(())", "(())()", "(()())", "((()))"]

Try this, i have modified your code a little bit. Modification and its explanation is marked in comments.
module.exports = Parentheses = (function() {
var _isParenthesesMatch = function(str) {
var parentheses = str.length;
var rightParentheses = '(';
var leftParentheses = ')';
var count=0;
for(i=0;i<str.length;i++){
//this is to check valid combination start always from ( and end with )
if(str.charAt(0)==rightParentheses && str.length-1==leftParentheses)
{
if(rightParentheses == str.charAt(i))
{
count++; //this will calculate how many times rightParentheses is present & increment count by 1
}
else if(leftParentheses == str.charAt(i))
{
count--; //this will simply decrement count to match valid sequence
}
}
if(count==0){
return true;
}
}
}());

Your function is wrong, try checking if left and right parenthesis and balanced:
function isValid(str){
var stripedStr = str.replace(/[^\(\)]+/g, '');
return stripedStr.split('').reduce(function(a, b){
return a > -1 ? b === '(' ? a + 1 : a - 1 : -1;
}, 0) === 0;
}
stripedStr - use replace() to remove any characters that are not ( or ).
split('') - returns an array so we can use reduce.
reduce() - applies a function against an accumulator and each value of the array (from left-to-right) has to reduce it to a single value.
The reduce starts with 0 as initial value and in the reduce function we count parenthesis
(+1 for (, -1 for ) )
Our string is valid if our counter never goes below 0 and we end up with 0.
You can write the reduce function like this too:
function(previousValue, currentValue){
if (previousValue > -1){
if (currentValue === '('){
return previousValue + 1;
} else {
return previousValue - 1;
}
}
return -1;
}
This is equivalent to:
function(a, b){
return a > -1 ? b === '(' ? a + 1 : a - 1 : -1;
}

It is wrong, because your function will return true for this example ))(( or this ())(()

Recursive function or loop in javascript?

I am trying to write a recursive function, but I am completely lost as to how to implement it. I currently have the following:
function change(p){
// code for function
}
var c1 = change(start);
var c2 = change(c1);
var c3 = change(c2);
// etc. etc.
Is there any way to do this with a while loop? For example:
while(currentResultofFunction != goal)
nestedly loop through as before until reaches true

function change(p) {
if (p != 1) { // your condition
change(p);
} else return p;
}

What about:
var val = start;
while(val) //or while val != goal
val = change(val);

What you are doing, is not recursive. You maybe mean iterative.
You can loop through the variables in this way:
var n = 2;
for (var i = 1; i <= n; i++) {
if (i == 1) window['c1'] = change(start);
else window['c' + i] = change(window['c' + (i - 1)]);
}

How to change a variable to something if it's undefined?

I don't have my script completed yet or anything so I can't post the code. Basically I need a variable to change and keep going through a function increasing by one until it reaches its destination. Something like:
function one(a) {
var x = a;
var max = 3;
if (a < 3) {
// some code
two(x);
} else {
// function will end here quitting the whole thing and possibly other code
}
}
function two(x) {
var change = x+1;
one(change);
}
It all works how I need it but when I first enter function one how would I make it so when x = a doesn't have a value that it will by default be 0?
something like...
function one(a) {
var x = a;
var max = 3;
if (x = undefined) {
x = 0;
} else {
if (x < 3) {
// some code
two(x);
} else {
// function will end here quitting the whole thing and possibly other code
}
}
}
function two(x) {
var change = x+1;
one(change);
}
Any ideas?

You could do this:
function one(a) {
var x = a || 0;
if (x < 3) {
//debugger;
two(x);
} else {
// function will end here quitting the whole thing and possibly other code
alert('Done');
}
}
function two(x) {
x++;
one(x);
}
one();
FIDDLE
var x = a || 0 means x is a if a can be asserted as true or 0.
x++ means x = x + 1

You can check to see if the variable is defined and send it in the functions argument by using the short hand conditional.
typeof(a)=="undefined" ? 0 : a;
You can change your code to:
function one(a) {
var x = (typeof(a)=="undefined" ? 0 : a);
var max = 3;
if (x < 3) {
// some code
two(x);
} else {
// function will end here quitting the whole thing and possibly other code
return;
}
}
Fiddle: http://jsfiddle.net/gBBL2/

var x = (typeof a === 'undefined') ? 0 : a;
If a is undefined, use 0. Otherwise use a as the value of x.