I was been asked in an interview to code for the following scenario.
var ele = [2,5,4,8,4,9].second();
If the above statement is written in javascript it ele should contain second highest element from that array. In this case it should contain 8.
how do you write the code for this? I assume we will have to write a function second()
but how do we call make sure it takes the array as that parameter?
Please help me with this. Thank You in advance.
That should get you started
Array.prototype.second = function() {
var biggest = -Infinity;
var second = -Infinity;
for (var i = 0; i < this.length; ++i) {
if (this[i] > biggest) {
second = biggest;
biggest = this[i];
} else if (this[i] < biggest && this[i] > second) {
second = this[i];
}
}
return second;
};
You should include error handling and there's plenty of room to optimize this solution.
Add a method to the Prototype of the Array Object.
Array.prototype.second = function() {
// Your logic here
}
Related
I started using a website called leetcode and one question is to remove all the duplicates in an array without create a new one. Here is the question https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/
My solution was to loop and the check each element against the next one, then if match use splice to remove the duplicated one. it works but not when you have something like [1,1,1,1,1] or [1,1,2,2,2,2,3,3] so I found on github a working code:
var removeDuplicates = function(nums) {
var i = 0;
for (var n in nums)
if (i === 0 || nums[n] > nums[i-1])
nums[i++] = nums[n];
return i;
};
This code works and passes all the 160 tests, but I don't understand clearly what is doing, especially the part in nums[i++] = nums[n]; can someone be so kind to help me to understand what this, simple, code is doing? thanks
Consider this code that creates a new array:
function removeDuplicates(nums) {
var res = [];
var i = 0;
for (var j=0; j<nums.length; j++)
if (i === 0 || nums[j] !== res[i-1])
res[i++] = nums[j];
return res;
}
The line you're asking about assigns nums[j] as new element at res[i] when the value is not the same as the previous one (res[i-1]), then increments i to put the next non-duplicate value in the next position.
Now we use the same algorithm but instead of assigning to a new res array, we modify the original nums array:
function removeDuplicates(nums) {
var i = 0;
for (var j=0; j<nums.length; j++)
if (i === 0 || nums[j] !== nums[i-1])
nums[i++] = nums[j];
nums.length = i; // drop the rest
}
Given that j >= i is guaranteed, we only modify array elements that we've always visited, so there's no harm in writing on the same array that we are reading from.
EDIT
Thank you guys, and i apologize for not being more specific in my question.
This code was written to check if a characters in the second string is in the first string. If so, it'll return true, otherwise a false.
So my code works, I know that much, but I am positive there's gotta be a better way to implement this.
Keep in mind this is a coding challenge from Freecodecamp's Javascript tree.
Here's my code:
function mutation(arr) {
var stringOne = arr[0].toLowerCase();
var stringTwo = arr[1].toLowerCase().split("");
var i = 0;
var truthyFalsy = true;
while (i < arr[1].length && truthyFalsy) {
truthyFalsy = stringOne.indexOf(stringTwo[i]) > -1;
i++
}
console.log(truthyFalsy);
}
mutation(["hello", "hey"]);
//mutation(["hello", "yep"]);
THere's gotta be a better way to do this. I recently learned about the map function, but not sure how to use that to implement this, and also just recently learned of an Array.prototype.every() function, which I am going to read tonight.
Suggestions? Thoughts?
the question is very vague. however what i understood from the code is that you need to check for string match between two strings.
Since you know its two strings, i'd just pass them as two parameters. additionally i'd change the while into a for statement and add a break/continue to avoid using variable get and set.
Notice that in the worst case its almost the same, but in the best case its half computation time.
mutation bestCase 14.84499999999997
mutation worstCase 7.694999999999993
bestCase: 5.595000000000027
worstCase: 7.199999999999989
// your function (to check performance difference)
function mutation(arr) {
var stringOne = arr[0].toLowerCase();
var stringTwo = arr[1].toLowerCase().split("");
var i = 0;
var truthyFalsy = true;
while (i < arr[1].length && truthyFalsy) {
truthyFalsy = stringOne.indexOf(stringTwo[i]) > -1;
i++
}
return truthyFalsy;
}
function hasMatch(base, check) {
var strOne = base.toLowerCase();
var strTwo = check.toLowerCase().split("");
var truthyFalsy = false;
// define both variables (i and l) before the loop condition in order to avoid getting the length property of the string multiple times.
for (var i = 0, l = strTwo.length; i < l; i++) {
var hasChar = strOne.indexOf(strTwo[i]) > -1;
if (hasChar) {
//if has Char, set true and break;
truthyFalsy = true;
break;
}
}
return truthyFalsy;
}
var baseCase = "hello";
var bestCaseStr = "hey";
var worstCaseStr = "yap";
//bestCase find match in first iteration
var bestCase = hasMatch("hello", bestCaseStr);
console.log(bestCase);
//worstCase loop over all of them.
var worstCase = hasMatch("hello", worstCaseStr);
console.log(worstCase);
// on your function
console.log('mutation bestCase', checkPerf(mutation, [baseCase, bestCaseStr]));
console.log('mutation worstCase', checkPerf(mutation, [baseCase, worstCaseStr]));
// simple performance check
console.log('bestCase:', checkPerf(hasMatch, baseCase, bestCaseStr));
console.log('worstCase:', checkPerf(hasMatch, baseCase, worstCaseStr));
function checkPerf(fn) {
var t1 = performance.now();
for (var i = 0; i < 10000; i++) {
fn(arguments[1], arguments[2]);
}
var t2 = performance.now();
return t2 - t1;
}
I've been looking for real world examples of recursion. Remember, programming Wizards, I'm and artist and in Photoshop scripting (scriptus modus operandi) it's normally used to loop over all layers and sub layers.
I'm working on a (simple) recursion script to solve a four digit combination lock. You know, start with 1, then try 2, then 3 etc until the solution is found. To make things easy in the example the second digit is correct so we know that we don't have to change that. Also the initial state the numbers start zero, but we know there are no zeroes in the final solution.
The attempt must match the solution AND also add up to 10 in order to
be solved.
This may seem a bit stoppid, but I want to put in a two part condition of the solution, mainly because I can then apply what I've learned and write a brute force suduko solver. But you must crawl before you can ice skate...
var puzzle = [0,2,0,0]; // source
var solution = [1,2,3,4];
var s = superCopy(puzzle); // working array
drawPuzzle(s);
solvePuzzle(s, puzzle);
var total = checkTotal(s, solution);
var solution = checkSolution(s, solution);
function checkTotal(arr, source)
{
var c = 0;
// count the total
for (var i = 0; i < arr.length; i++)
{
c += arr[i];
}
if (c == 10)
{
alert("Total OK")
return true;
}
}
function checkSolution(arr, source)
{
// check the solution
for (var i in arr)
{
if (arr[i] != source[i]) return false
return true;
}
}
function solvePuzzle(arr, source)
{
for (var i = 0; i < arr.length; i++)
{
// check the source
var sourceCell = source[i];
//alert("checking source " + sourceCell)
//if it's a zero we can change it
if (arr[i] == 0)
{
cell = arr[i];
cell+=1;
if (cell > 4) cell = 0;
arr[i] = cell;
}
}
// check the solution
for (var i in arr)
{
// overflow time!
if (arr[i] != source[i]) solvePuzzle(arr, source)
else
{
alert("All done!")
}
}
}
function drawPuzzle(arr)
{
var p = "";
var c = 0;
for (var i = 0; i < arr.length; i++)
{
if (arr[i] == 0) p += "-"
else p += arr[i];
c+=1;
}
alert(p);
}
function superCopy(arr)
{
// returns a true copy of an array
tempArr = new Array();
for (var i = 0; i < arr.length; i++)
{
if (arr[i] == 0) tempArr[i] = 1 // changed, thanks Nostradamnit!
else tempArr[i] = arr[i]
}
return tempArr
}
The script is incomplete. This what I have so far, it falls over with an overflow error. Note solvePuzzle and checkTotal functions are not called because I realised that solvePuzzle needs to call itself and work out the solution...which is when I ran into overflow problems and got a bit confused.
I realise that this type of question runs dangerously close to a "fix my code" venture, so I'm prepared to put a bounty out for it. Thanks.
There are a couple of problems with your code. First up, your checkSolution function stops at the very first number that matches. You probably want it to check every number before returning true, so you should move return true outside the for loop. It only gets there if all numbers match up.
Another flaw is the superCopy function, which as Nostradamnit pointed out has a flawed condition.
Your next problem is in solvePuzzle, where you have this:
if (arr[i] == 0)
{
cell = arr[i];
cell+=1;
if (cell > 4) cell = 0;
arr[i] = cell;
}
The thing is, because arr[i] is 0 and you only add 1, cell will never be 4. So your if is never going to fire. This is where your infinite loop is: it only increments values that are zero with one, so after all zeros became one, it never goes further and you keep checking if "1111" is the solution.
Now the overflow: you shouldn't be calling solvePuzzle for every cell, this grows exponentially:
for (var i in arr)
{
// overflow time!
if (arr[i] != source[i]) solvePuzzle(arr, source)
else
{
alert("All done!")
}
}
Also, you never check the result again, so the looping never ends. You would probably want to change this to this:
if(checkTotal(arr) && checkSolution(arr, source))
{
alert("All done!");
return;
}
solvePuzzle(arr, source);
As a side note (not a bug causing thing): your checkTotal function isn't using the source parameter, so you can probably leave that out. Also, there is a rogue variable called cell in solvePuzzle, which isn't a big deal in this case, but it would be better to put var in front of it so it doesn't become global. Also, there is a sourceCell variable that never gets used.
At first glance, it seems that your superCopy function is flawed. You create an empty array, then compare its 0 index (which doesn't exist) to the input array. Is that where you are getting your "overflow"?
The problem seems to be that you call solvePuzzle(arr, source) multiple times in the same iteration:
for (var i in arr)
{
// overflow time!
if (arr[i] != source[i]) solvePuzzle(arr, source)
else
{
alert("All done!")
}
}
So you iterate over every item in the array, and if it is not equal to the source item, you call solvePuzzle again. But if you have several items that don't match, solvePuzzle will get called multiple times on the same array. And for each call, it gets called again multiple times. Therefore your function calls grow exponentially and result finally in a stack overflow.
What you probably intended to do, is the following:
var areArraysEqual = true;
for (var i in arr)
{
if (arr[i] != source[i]) {
areArraysEqual = false;
break;
}
}
if (areArraysEqual) {
alert("All done!");
} else {
solvePuzzle(arr, source);
}
I haven't looked over your solution yet, but i did write a recursive one for myself to solve the problem. Perhaps it can be of help as a guideline?
var solution = [1,2,3,4];
function checkSolution(arr) {
return solution.every(function(item, index){ return item === arr[index]; });
}
function increment(arr) {
for (var i=0; arr[i] === 9; i++) {
arr[i] = 0;
}
arr[i]++;
return arr;
}
function solvePuzzle(arr) {
if (isNaN(arr[arr.length-1])) {
return null;
}
if (checkSolution(arr)) {
return arr;
}
return solvePuzzle(increment(arr));
}
var solution = solvePuzzle([1,1,1,1]);
console.log(solution); // [1,2,3,4]
Maybe little bit off topic but I have created the easiest recursion example possible in my opinion.
http://jsfiddle.net/33yfS/
var str = "9785";
function rec(a, b)
{
var c=0;
if(b==-1)
return "";
if(a!=str.charAt(b))
return rec(a+1, b);
else
{
return rec(0,b-1)+""+a;
}
}
var ans = rec(0,str.length-1)
Hi all I'm learning Javascript with the Stoyan Stefanov's book. I'm stuck on Chapter 4 Exercise 4:
Imagine the String()constructor didn't exist. Create a constructor
function MyString()that acts like String()as closely as possible.
You're not allowed to use any built-in string methods or properties,
and remember that String()doesn't exist. You can use this code to
test your constructor:
>>> var s = new MyString('hello');
>>> s[0];
"h"
I can't think on a way to achieve "s[0]", at least not with the knowledge I have now.
Any thoughts?
Thanks
Objects can have properties of themselves defined using array like syntax. String chars can be accessed with array like syntax.
function MyString (str) {
this.length = 0; // string length
var i = 0;
while(str[i] != undefined) {
this.length++;
i++;
}
for (var i=0; i< this.length;i++)
{
this[i]=str[i];
}
}
var s=new MyString('hello');
alert(s[0]); //h
here is my solution for this exercice :
function MyString(msg){
var array_msg = msg.split("");
array_msg.toString = function(){
return array_msg.join("");
};
array_msg.valueOf = function(){
return array_msg.toString();
};
array_msg.charAt = function(i){
if(array_msg[i] === undefined){
return array_msg[0];
}else{return array_msg[i];}
};
array_msg.concat = function(msg2){
return array_msg.join("")+" "+msg2;
};
array_msg.slice = function(d,f){
var res = "";
if(f<0){
f = array_msg.length + f;
}
for(var i=d; i<f; i++){
res += array_msg[i]
}
return res;
};
array_msg.split = function(el){
return array_msg.toString().split(el);
};
return array_msg;
}
A slight variation of the above...more of a tweak than anything
var MyString = function (s) {
for (var i = 0; i < s.length; i++){
this[i] = s[i]
}
this.length = function() .....
You also don't need to assign it to anything as extra as the comment suggests. this[i] will be created for the length of the string passed to s
EDIT:
Part of the question in the book says not to use existing string methods so can't use charAt so I've switched it to s[I]
This is another variation of one of the above solutions but instead of using a for loop I am using a while loop. I don't usually use while loops for these kinds of things but it worked really well here.
Adding the length property is optional.
function MyString(str) {
this.length = 0; // Creating an optional length property
this.value = str;
var i = 0;
while(str[i] != undefined) {
this[i] = str[i];
this.length++;
i++;
}
}
var name = new MyString('billy');
console.log(name.value); // 'billy'
console.log(name[0]); // 'b'
console.log(name.length); // 5
I have a problem with this script, something is going wrong.
Rnumer stays undefined.This script should return and write all uneven digits from the random number list. Can someone tell me what I do wrong. Thanks in advance
var Rnumber = new Array();
for (i = 0; i<= 100;i++)
{
Rnumber[i] = Math.ceil(Math.random()*101);
// document.write(Rnumber[i] + "<br/>");
}
function unevenAndDivisible(Rnumber)
{
var remainder = new Array();
for (i = 0; i<= 100; i++)
{
remainder = parseInt(Rnumber[i])%2;
}
return remainder;
}
document.write(unevenAndDivisible());
Changed to
var Rnumber = new Array();
for (i = 0; i<= 100;i++)
{
Rnumber[i] = Math.ceil(Math.random()*101);
// document.write(Rnumber[i] + "<br/>");
}
function unevenAndDivisible(Rnumber)
{
var remainder = new Array();
for (i = 0; i<= 100; i++)
{
remainder[i] = Rnumber[i]%2;
}
return remainder;
}
document.write(unevenAndDivisible(Rnumber));
but now i get the result :
0,1,0,0,1,0,0,0,1,1,0,0,1,0,1,1,1....
I simply want maybe I asked it wrong the first time, to write al uneven numbers from the random list of Rnumbers
Then I need to divide that through 7 and return that.
EDIT
Allmost all problems are clear , thanks everyone for that.
Their is still one question left:
In this code below it only take the first uneven value from remainder and I want that it takes all values that are uneven to the next if statement to check %7.
Maybe you see the problem better if you run it for youreself
var Rnumber = new Array();
for (i = 0; i<= 100;i++)
{
Rnumber[i] = Math.ceil(Math.random()*101);
}
function unevenAndDivisible()
{
var remainder = [];
var answer = [];
for (i = 0; i<= 100; i++)
{
if (Rnumber[i]%2 !== 0)
{
remainder.push(Rnumber[i]);
for (c = 0; c <= remainder.length;c++)
{
if (remainder[c]%7 == 0)
{
answer.push(remainder[c]);
}
}
}
}
return answer;
}
answer = unevenAndDivisible();
document.write(answer);
Problem solved , Thanks everyone
You don't need to pass Rnumber to the function, as it's already available in scope:
function unevenAndDivisible()
{
var remainder = [];
for (i = 0; i<= 100; i++)
{
if (Rnumber[i]%2 !== 0) {
remainder.push(Rnumber[i]);
}
}
return remainder;
}
remainder = unevenAndDivisible();
console.log(remainder);
JS Fiddle demo.
Edited in response to question from OP (in comments to question, above):
...can someone explain what this mean: var remainder = [];
Sure, it's array-literal notation, which is equal to: var remainder = new Array();, it's just a little more concise, and I prefer to save myself the typing. I get the impression, from JS Lint, whenever I use var x = new Array(); therein that the above version is generally preferred (since it complains otherwise), but I don't know why.
Either pass Rnumber to the function unevenAndDivisible or omit it from the argument list. Since it is an argument, it has more local scope than the initial declaration of Rnumber.
Your problem is the line
function unevenAndDivisible(Rnumber)
You are passing in Rnumber in as an argument, but when you call unevenAndDivisible()
you are not passing it it.
Consequently for the body of the function Rnumber is undefined (cause you passed nothing in)
The following snippet is equivalent to what you wrote nad might explain better
function unevenAndDivisible(xyz)
{
var remainder = new Array();
for (i = 0; i<= 100; i++)
{
remainder = parseInt(xyz[i])%2;
}
return remainder;
}
then called as
unevenAndDivisible(undefined)
to fix it remove the argument from the call definition
i.e. define it as
function unevenAndDivisible()
1 - you is not defining the Rnumber value that's function argument.
2 - in loop, you're defining remainder to divised value of ranumber and is not saving in array; try:
change:
remainder = parseInt(Rnumber[i])%2;
to
remainder[i] = parseInt(Rnumber[i])%2;
var array = [],
i = 100;
while (i--) {
var random = Math.random()*i|0;
if(random % 2)
array.unshift(random);
}
alert(array);