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.

Hide Tags

 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--];        }    }};