I'm working on JavaScript algorithms and could use some help. What am I doing wrong exactly?
// Given an array of arr, positive integers, and another number X.
// Determine whether or not there exist two elements in arr whose sum is exactly X.
function keyPair(arr, x){
var sum=false;
var key=0;
var temp=0;
for(var i=0;i<=arr.length;i++){
while(sum=false){
key=arr[i];
arr[i]=temp;
temp=key;
}
if(temp+arr[i]==x){
sum=true;
}
}
console.log(sum);
}
keyPair([1,2,4,3,6], 4);
I think this one deserves an explanation:
sum=false is an assignment statement. As an expression, an assignment statement is evaluated as undefined (regardless of the value assigned). So while(sum=false) is actually while(undefined), which is interpreted as while(false).
Your mistake was - as explained multiple times - the wrong comparison operator. I took the liberty of rewriting your code involving a .reduce() call:
function keyPair(arr,sum){
return arr.reduce((a,c,j)=>{
let i=arr.indexOf(sum-c);
if (i>-1 && j<i) a.push([c,arr[i]]);
return a;}, []);
}
console.log(keyPair([1,2,4,3,6], 5));I'm not going to repeat what has been already said about your code. But even if you're starting coding in JS, it pays for you to start using JS built-ins that will save you a lot of time:
// Determine whether or not there exist two elements in arr whose sum is exactly X.
So you're only interested in whether they exist, not in which are those:
const keyPair = (arr,value) =>
// some: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some
// slice: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice
arr.some( (x,i) => arr.slice(i).some( y => x + y === value));
console.log(keyPair([1,2,4,3,6], 4))
console.log(keyPair([1,1,1,1,1], 4))With some you check if there is an x+y sum that equals to your desired value
With slice you omit the portion of the array that you don't need to check