[LeetCode] Merge Sorted Array

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本文介绍了一种将两个已排序的整数数组A和B合并为一个有序数组的方法。通过从数组尾部开始比较并放置较大元素的方式进行归并，避免了从头部开始归并时可能产生的大量元素移动。

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 to hold additional elements from B. The number of elements initialized in A and B are m and n respectively.

归并数组 A[] B[] ，A有足够的空间放下B;

如果从左往右归并的话，会需要移位（将A的数组后移)

所以可以考虑从右往左归并。

三个指针：

k : 结果数组的指针，初始指向结果数组末尾也即A[k] k = m+n-1;

pa: 指向A数组中元素的指针, 初始指向A末尾 pa = m-1;

pb: 指向B数组中元素的指针，初始指向B末尾 pb = n-1;

三个指针不断前移，直到pa == 0 ,pb == 0

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(n <= 0) return ;
        int k = m+n-1;
        int pa = m-1;
        int pb = n-1;
        while(pa >= 0 && pb >= 0) {
            A[k--] = A[pa] > B[pb] ? A[pa--] : B[pb--];
        }
        while(pb >= 0) A[k--] = B[pb--];
    }
};