failed

merge_sort.go

func merge(nums1 []int, m int, nums2 []int, n int)  {
    j := n-1
    if m == 0 {
        for i := len(nums1)-1; i >= 0; i-- {
            nums1[i] = nums2[j]
            j--
        }
    }
    
    k := len(nums1)-1
    
    for i := m-1; i >= 0; i-- {
        if j < 0 {
            nums1[k] = nums1[i]
            k--
        } else if nums1[i] > nums2[j] {
            nums1[k] = nums1[i]
            k--
        } else if nums1[i] < nums2[j] {
            nums1[k] = nums2[j]
            k--
            j--
            i++ // to maintain the current i position
        } else if nums1[i] == nums2[j] {
            nums1[k] = nums1[i]
            k--
        }
    }
    
    if j >= 0 {
        for k >= 0 {
            nums1[k] = nums2[j]
            k--
            j--
        }
    }
}

1, Line 2: m == 0 does not imply n==1
2. What happens if j >= 0 after the main loop?

nums1.length == m + n

Implies that the length is 1 if m==0 because we must have a spot for num2's number, then n must be 1. Right?

There's also this example:

Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Explanation: The arrays we are merging are [] and [1].
The result of the merge is [1].
Note that because m = 0, there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1.

But maybe I'm misreading this @CollinShoop

Ahh I see what you're saying. For example n could be 5 and m 0..

fixed now