排序（一）归并排序

//merge sort
//合并有序序列
//没有改变相等元素的前后位置
#include<iostream>
#include<vector>
using namespace std;
void merge(vector<int>& v, int left, int right, int right_end) {
    int* v2 = new int[right_end - left + 1];//用（）会内存泄露
    int s_start = left;
    int start = left;
    int left_end = right - 1;
    while (left <= left_end && right <= right_end) {
        if (v[left] <= v[right]) {
            v2[s_start++] = v[left++];
            //合并进临时数组（且按照排序范围的下标）
        }
        else {
            v2[s_start++] = v[right++];
        }
    }
    while (left <= left_end) {//将某方剩余的合并进s
        v2[s_start++] = v[left++];
    }
    while (right <= right_end) {
        v2[s_start++] = v[right++];
    }
    for (int i = start; i <= right_end; i++) {
        v[i] = v2[i];
    }
}
void msort(vector<int>& v, int left, int right) {
    if (left >= right) {//只剩最后一个时
        return;
    }
    int mid = (left + right) / 2;
    msort(v, left, mid);
    msort(v, mid + 1, right);//排完左边排右边
    //排完合并
    merge(v, left, mid + 1, right);//此时用到vector s,在参数中给出左边一半的起点终点，的起点，终点
//可以不给出mid，因为右半起点-1就是左半终点

}
void  mergsort(vector<int>& v) {
    int size = v.size();
    if (v.size() == 0) {
        return;
    }
    msort(v, 0, size - 1);//指明排序范围
}


int main()
{
    vector<int> a{ 1,5,7,4,3,8,5,1,2,99,242,241 };
    mergsort(a);
    for (int i = 0; i < a.size(); i++) {
        cout << a[i] << "  ";
    }
}