Why aren't the 0s being spliced out when merging a sorted array?

Question

I'm working on this challenge:

https://leetcode.com/problems/merge-sorted-array/

This is my code:

/**
 Do not return anything, modify nums1 in-place instead.
 */
function merge(nums1, m, nums2, n) {
    nums2.forEach(i => {
        if (i > 0) {
            nums1.push(i)
        }

    })

    nums1.sort()


    for (let i = 0; i < nums1.length; i++) {
        if (nums1[i] == 0) {
            nums1.splice(i, 1)
        }
    }
};

This is the input ([1,2,3,0,0,0], 3, [2,5,6], 3)

My output is: [0,1,2,2,3,5,6]

Instead of: [1,2,2,3,5,6]

Can you tell me why?

Thanks!

Answer 1

you're looping over an array and using the index of the original array, but the array itself is being changed.

So, if you start with [0,0,0,1,2,2,3,5,6], and you remove at index 0, [0,0,1,2,2,3,5,6]. Then i=1, you check and remove at index 1 [0,(here=>)0,1,2,2,3,5,6] and end up with [0,1,2,2,3,5,6]. Further indexing reveals no zeroes.

I would suggest you use a reduce or map instead and create a new array while maintaining the original for indexing.

Answer 2

In your code you are altering the nums1 array length (by using the splice method) while looping over it using its initial length. This causes some indexes to be skipped. Adding i-- after you splice the array should solve your issue.

function merge(nums1, m, nums2, n) {
    nums2.forEach((i) => {
        if (i > 0) {
            nums1.push(i);
        }
    });

    nums1.sort();

    for (let i = 0; i < nums1.length; i++) {
        if (nums1[i] == 0) {
            nums1.splice(i, 1);
            i--;
        }
    }
}