Recursion to sum the array! what is wrong with my code?

Question

just trying to find the sum in the array and can't figure out what is wrong with my code, if you can help that would be appreciated :)

function arraySum(arr, index) {
    if (arr.length <= index)
        return 0;
    return (arraySum(arr, arr.length - 1) + arr[arr.length - 1]);

}

I'm trying to find the sum of the array using recursion. what is exactly wrong with my code :) if you can help that would be appreciated

ps index=0 arr.length =8

Answer 1

function arraySum(arr, index) {
    if (index >= arr.length)
        return 0;
    return (arraySum(arr, index + 1) + arr[index]);
}

arr.length - 1 is the same, what you need to do is to iterate through the array, to make it work recursively. recursion needs a terminating point. in your code you are passing arr.length - 1 as index at every call, which remains constant.

Answer 2

First of all, in the recursion patterns you need a break condition.

Second, in each step of the recursion you need to take a little piece of work, and pass the rest to the others.

You have the break condition but it seems like your little piece of work is missing or not done properly.

Here is how to do that:

var sum = function(arr, currentIndex) {
   if(currentIndex < 0 || currentIndex >= arr.length) return 0;
   return arr[currentIndex] + sum(arr, ++currentIndex);
};

//Test it
var arr = [1, 4, 5];
sum(arr, 0);

Answer 3

Note: There are much better ways of achieving the desired goal:
How to find the sum of an array of numbers

---

To answer OP's question, here's an other approach using pop():

• If there are more then items in the array (arr.length > 1)

  • Return recursive result:
    (arr.pop() + arraySum(arr))

• If this was the last item, just return the last value
  arr.pop()

Combining this in a short-if-statement gives us:

function arraySum(arr) {
    return (arr.length > 1) ? (arr.pop() + arraySum(arr)) : arr.pop();
}

---

function arraySum(arr) {
    return (arr.length > 1) ? (arr.pop() + arraySum(arr)) : arr.pop();
}

const arr = [ 1, 2, 3 ];
const res = arraySum(arr);
console.log(res); // 6

Answer 4

I tried the following snippet of code and it is running

function arraySum(arr, index) {
  if (index >= arr.length) {
    return 0;
  }
  return arr[index] + arraySum(arr, index + 1)  ;
}
const x = arraySum([1, 2, 3], 0);
console.log(x);

Since this is a simple array if you just need sum you can use reduce method

function sum(arr) {
  const reducer = (sum, val) => sum + val;
  const initialValue = 0;
  return arr.reduce(reducer, initialValue);
}

sum([1, 3, 5, 7]); // 16

Answer 5

function findSum(A, N) {
    if (N <= 0)
        return 0;
    return (findSum(A, N - 1) + A[N - 1]);
}

 
let A = [1, 2, 3, 4, 5];
let N = A.length;
document.write(findSum(A,N));