Equal sides of an array in JS-CodePudding

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

CodePudding user response：

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]))

CodePudding user response：

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>