归并排序（模板题）

题目链接：

https://www.acwing.com/problem/content/description/789/

 

题解：

1、找分界点。

2、分别排序

3、归并

递归实现

 

AC代码：

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const int N = 1e5+5;
int a[N],tmp[N];


void merge_sort(int a[],int l,int r){
    if(l >= r) return;
    
    int mid = (l+r) / 2;
    
    merge_sort(a,l,mid);
    merge_sort(a,mid+1,r);
    
    int s1 = l,s2 = mid+1;
    int s = 0;
    while(s1 <= mid && s2 <= r){
        if(a[s1] <= a[s2]) tmp[s++] = a[s1++];
        else tmp[s++] = a[s2++];
    }
    
    while(s1 <= mid) tmp[s++] = a[s1++];
    while(s2 <= r) tmp[s++] = a[s2++];
    
    for(int i=l,j=0;i<=r;j++,i++) a[i] = tmp[j];
}


int main(){
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++) scanf("%d",&a[i]);
    merge_sort(a,0,n-1);
    for(int i=0;i<n;i++) printf("%d ",a[i]);
    return 0;
}