recursive function return different values depending of order when summing array elements

Question

I implemented the following recursive JS function to get the the sum of elements in a array. This function works fine, when input [1,2,3] it returns 6, which is OK.

function sumOfNumbers(array) {
    if (array.length == 1) {
        return array[0];
    } else {
        last = array.length - 1;
        return array[last] + sumOfNumbers(array.slice(0, last));
    }
}

However, when changing the order of the sum to:

    return sumOfNumbers(array.slice(0,last)) + array[last];

It returns 5 for [1,2,3]. Does anybody knows why?

Why are you doing this recursively anyway? Wasted memory, just use a loop. — Etheryte
– Etheryte, Commented Apr 9, 2014 at 16:51

Gerrat · Accepted Answer · 2014-04-09 15:49:01Z

3

Because the variable last is global, and you're changing it with your call to sumOfNumbers(array.slice(0,last)), before this part: array[last] sees it.

answered Apr 9, 2014 at 15:49

Gerrat

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1 Comment

Javier Giovannini Over a year ago

It is actually true, thank you! I changed to var last and works well in any order.

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