Merge two Sorted Arrays Without Extra Space

[Question]: Given two sorted arrays arr1[] and arr2[] ofsizes n and m in non-decreasing order. Merge them in sorted order without using any extra space. Modify arr1 so that it contains the first N elements and modify arr2 so that it contains the last M elements.

Example 1:

Input: 
n = 4, arr1[] = [1 3 5 7] 
m = 5, arr2[] = [0 2 6 8 9]
Output: 
arr1[] = [0 1 2 3]
arr2[] = [5 6 7 8 9]
Explanation:
After merging the two 
non-decreasing arrays, we get, 
0 1 2 3 5 6 7 8 9.

Example 2:

Input: 
n = 2, arr1[] = [10 12] 
m = 3, arr2[] = [5 18 20]
Output: 
arr1[] = [5 10]
arr2[] = [12 18 20]
Explanation:
After merging two sorted arrays 
we get 5 10 12 18 20.

/**
 Time Complexity: O((n+m)*log(n+m)), where n and m are the sizes of the given arrays.
 Reason: The gap is ranging from n+m to 1 and every time the gap gets divided by 2. So, the time complexity of the outer loop will be O(log(n+m)). Now, for each value of the gap, the inner loop can at most run for (n+m) times. So, the time complexity of the inner loop will be O(n+m). So, the overall time complexity will be O((n+m)*log(n+m)).

 Space Complexity: O(1) as we are not using any extra space.
 */
func mergeTowSortedArrays(_ arr1: inout [Int], _ arr2: inout [Int], _ n: Int, _ m: Int) {
    
    var len = n + m
    var gap = len / 2
    
    while gap > 0 {
        var left = 0
        var right = left + gap
        
        while right < len {
            if left < n && right >= n {
                swapIfGreater(&arr1, &arr2, left, right - n)
            } else if left >= n {
                var newArr2 = arr2
                swapIfGreater(&arr2, &newArr2, left - n, right - n)
            } else {
                var newArr1 = arr1
                swapIfGreater(&arr1, &newArr1, left, right)
            }
            left += 1
            right+=1
        }
        
        if gap == 1 { break }
        
        gap = (gap / 2) + (gap % 2)

    }
    
    func swapIfGreater(_ arr1: inout [Int], _ arr2: inout [Int], _ ind1: Int, _ ind2: Int) {
        if arr1[ind1] > arr2[ind2] {
            (arr1[ind1], arr2[ind2]) = (arr2[ind2], arr1[ind1])
        }
    }
}

var arr1 = [1, 4, 8, 10]
var arr2 = [2, 3, 9]
var n = 4, m = 3

mergeTowSortedArrays(&arr1, &arr2, n, m)

print("The merged arrays are:--", arr1, arr2)// [1, 2, 3, 4] [8, 9, 10]