leetcode || 88、Merge Sorted Array

problem：

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 mand n respectively.

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Array Two
Pointers

题意：原址合并两个已序数组

thinking：

（1）先合并再排序，O（m+n）lo(m+n)

(2)从后往前比较插入，不用移动元素，O（m+n）

code：

合并排序

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        for(int i=0;i<n;i++)
            A[m+i]=B[i];
        sort(A,A+m+n);
    }
};

从后往前比较插入

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int index = m + n - 1;
        int aIndex = m - 1;
        int bIndex = n - 1;
        while(0 <= aIndex && 0 <= bIndex)
        {
            if (B[bIndex] > A[aIndex])
            {
                A[index--] = B[bIndex--];
            }
            else
            {
                A[index--] = A[aIndex--];
            }
        }

        while(0 <= aIndex)
        {
            A[index--] = A[aIndex--];
        }

        while(0 <= bIndex)
        {
            A[index--] = B[bIndex--];
        }
    }
};