归并排序

时间复杂度（N*logN）

#include<iostream>	
#include<stdio.h>
#include<vector>
using namespace std;
int a[100];
vector<int>ve;
void merge(int* x, int L, int mid, int R) {
	int p1, p2;
	p1 = L;
	p2 = mid + 1;
	while (p1 <= mid && p2 <= R) {
		ve.push_back(x[p1] < x[p2] ? x[p1++] : x[p2++]);
	}
	while (p1 <= mid) {
		ve.push_back(x[p1++]);
	}
	while (p2 <= R) {
		ve.push_back(x[p2++]);
	}
	
	for (int i=0; i < ve.size(); i++) {//将排好序的数据拷贝到原来数组中去
		x[L + i] = ve[i];
	}
}
int Pai(int* arr, int L, int R) {
	if (L == R)
		return arr[L];

	int mid = (L + R) / 2;
	Pai(arr, L, mid);//将整个区间的左区间排序
	Pai(arr, mid + 1, R);//有区间排序
	ve.clear();
	merge(arr, L, mid,R);//借助ve数组将连个区间重新排序
}
int main()
{
	int n;
	cout << "输入要排序的个数：";
	cin >> n;
	cout << "输入要排序的数，用空格隔开:";

	for (int i = 0; i < n; i++) 
		cin>>a[i];
	
	Pai(a, 0, n - 1);
   
	for (int i = 0; i < n; i++)
		cout << a[i] << ' ';
	

	return 0;
}