Recursive SUM function javascript

Question

I have been given the function below in pseudocode and I am trying to translate it to JS, but I keep getting an infinity loop.

Update

Thanks zord, mid fixed the recursion issue. Now I get the wrong sum, any suggestions?

What am I doing wrong?

function SUM(arr, left, right){
  
    if(left > right){ 
        return 0 
    }
    else if(left == right){
      return arr[left]
    }

    mid = Math.floor((left + right) / 2);

    lsum = SUM(arr,left,mid);
    rsum = SUM(arr,mid+1,right); 

    return lsum + rsum

}

arr = [1,2,3,4,5]
left = 0;
right = arr.length - 1;


console.log(SUM(arr, left, right));

Thanks!

I suspect you just need to declare your variables mid, lsum, and rsum instead of having them as implicit globals — VLAZ
– VLAZ, Commented Dec 15, 2021 at 20:11

zord · Accepted Answer · 2021-12-15 20:32:52Z

1

mid should be halfway between left and right:

mid = Math.floor((left + right) / 2);

Also, you need to make your variables block scoped as VLAZ mentioned. Otherwise they will be global, and overwritten by different runs of the function.

const mid = Math.floor((left + right) / 2);

const lsum = SUM(arr, left, mid);
const rsum = SUM(arr, mid + 1, right);

edited Dec 15, 2021 at 20:32

answered Dec 15, 2021 at 20:15

zord

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1 Comment

etevou Over a year ago

Thanks @zord! That fixed the loop. Getting 17 for the SUM instead of 15. Any suggestions?

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