88. Merge Sorted Array

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

Note:

  • The number of elements initialized in nums1 and nums2 are m and n respectively.
  • You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2.

Example:

Input:
nums1 = [1,2,3,0,0,0], m = 3
nums2 = [2,5,6],       n = 3

Output: [1,2,2,3,5,6]
Code
Think smart! Instead of keeping pointers to the start. Keep the pointers at the end.
public class Problem88 {

    public void merge(int A[], int m, int B[], int n) {
        // Handle Edge cases
        if (A == null || B == null || n == 0) {
            return;
        }

        // Three pointers
        // Pointer1 pointing to the last element in A
        // Pointer2 pointing to the last element in B
        // Pointer3 pointing to the last index in A
        int i = m - 1;
        int j = n - 1;
        int k = m + n - 1;

        while (i >= 0 && j >= 0) {
            if (A[i] >= B[j]) {
                A[k--] = A[i--];
            } else {
                A[k--] = B[j--];
            }
        }

        while (j >= 0) {
            A[k--] = B[j--];
        }
    }

}
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