Merge Sorted Array

sorted 数组, 常用二指针遍历, 会倒叙, 会前序

Given two sorted integer arrays A and B, merge B into A as one sorted array.

 Notice

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.

Have you met this question in a real interview? Yes
Example
A = [1, 2, 3, empty, empty], B = [4, 5]

After merge, A will be filled as [1, 2, 3, 4, 5]

Tags 
Sorted Array Array Facebook
Related Problems 
Easy Space Replacement 18 %
Easy Merge Two Sorted Arrays

逆序遍历的好处,

1只遍历后面的

2此题在于空间上可以不干扰.

public void mergeSortedArray(int[] A, int m, int[] B, int n) {
        int i = m-1, j = n-1, index = m + n - 1;
        while (i >= 0 && j >= 0) {
            if (A[i] > B[j]) {
                A[index--] = A[i--];
            } else {
                A[index--] = B[j--];
            }
        }
        while (i >= 0) {
            A[index--] = A[i--];
        }
        while (j >= 0) {
            A[index--] = B[j--];
        }
    }