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Equal sides of an array in JS

Question: Take an array with integers and find an index N where the sum of the integers to the left of N is equal to the sum of the integers to the right of N. If there is no index that would make this happen, return -1. Let's say you are given the array {1,2,3,4,3,2,1}: Your function equalsides() will return the index 3, because at the 3rd position of the array, the sum of left side of the index ({1,2,3}) and the sum of the right side of the index ({3,2,1}) both equal 6.

I have written the following

Declare two variables mid and i where mid the index we are looking for i= this is starting index
Then while (mid<= arr.length-1) we will go through the array and add up each side of the array one side from i=0 to i=mid and then from i=mid to i=array.length-1, while adding up each side to leftSum and rightSum respectively
And if leftSum==rightSum in any of these instances we will return mid if it didnt it will increase mid by one and reiterate ,
If mid is not returned we will return -1 at the end.

In code it is the following

function findEvenIndex(arr)
{
  //Code goes here!
  let mid =1;
  let leftSum=0;
  let rightSum=0;
  while(mid<(arr.length-1)){
   
      
    for(i=0;i<mid;i++){
      
        leftSum=leftSum+arr[i]
      
    }
    
    rightSum = rightSum + arr[mid]
 
 
    if(rightSum==leftSum){
        console.log("mid: "+ mid);
        return mid;
    }
    else{
        
        mid++;
        
    }

  }
 return -1;
}

however I am not sure why this is not working, any help would be appreciated

7 months ago · Juan Pablo Isaza

3 answers

Answer question

0

The easiest thing is to use slice + reduce to find the start and end sum for that index

function findEvenIndex(arr) {
  let index = -1;
  for (var i = 0; i < arr.length; i++) {
    let start = arr.slice(0, i+1).reduce((a, b) => a + b, 0);
    let end = arr.slice(i).reduce((a, b) => a + b, 0)
    if (start === end) {
      index = i
    }
  }
  return index;
}

console.log(findEvenIndex([1,2,3,4,3,2,1]))

7 months ago · Juan Pablo Isaza Report

0

A slightly different approach

function findEvenIndex(arr) {
  let left = 0, right = arr.reduce((a, b) => a + b, 0);
  for (let i = 0; left <= right; ++i) {
    right -= arr[i];
    if (left === right) {
      return i;
    }
    left += arr[i];
  }
  return -1;
}

console.log(findEvenIndex([1, 2, 3, 4, 3, 2, 1]))

7 months ago · Juan Pablo Isaza Report

Answer question

Find remote jobs

Accepted Answer · 2022-07-03T08:44:20.364Z

const inputElement = document.querySelector("#input")
const button = document.querySelector("#btn")
const resultElement = document.querySelector("#result")

button.addEventListener("click" , ()=>{

if(!inputElement.value || inputElement.value.split(",").length <3){ return; }

const numbers = inputElement.value.split(",").map(number=>Number(number))


resultElement.textContent = findIndexOfEqualSum([...numbers])

})

function findIndexOfEqualSum(arr) {

    
    for(let i=0; i < arr.length -1; i++){
    
        let leftSide=0
        let rightSide=0
        
        for(j=0 ; j < i; j++){
        leftSide+= arr[j]
        }
        
        for(g=i+1 ; g < arr.length; g++){
        rightSide+= arr[g]
        }
        
        
        if(leftSide==rightSide) return i;
        
    }
    
   return -1;
}

<body>
<style>
body>*:not(:last-child) {
margin-bottom: .5rem;
}

#input {
display:block;
width:100%;
padding:.5rem;
}
</style>

<input 
id="input" 
type="text" 
placeholder="enter comma seperated numbers"
>

<button id="btn"> Find Index </button>

<div id="result"> Result will be here </div>

</body>