LeetCode - Merge Sorted Array | Darren's Blog

Given two sorted integer arrays A and B, merge B into A as one sorted array.
Note: You may assume that A has enough space (size that is greater or equal to m + n) to hold additional elements from B. The number of elements initialized in A and B are m and n respectively.
The best solution is to work backwards for both arrays. We use the two indices as before, but initialize them to the indices of the last effective number, i.e. m-1 and n-1. 

public void merge(int A[], int m, int B[], int n) {

        if (A == null || B == null)

            return;

        int i = m - 1, j = n - 1, k = m + n - 1;

 

        // Put the larger one into A in reverse order

        while (i >= 0 && j >= 0) {

            if (B[j] >= A[i])

                A[k--] = B[j--];

            else

                A[k--] = A[i--];

        }

 

        // Remaining numbers in B are the smallest

        while (j >= 0)

            A[k--] = B[j--];

    }

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