1 确定分界点 mid （l+r）/2

2 递归排序left right 

3 归并 合二为一

 

#include<bits/stdc++.h>
using namespace std;
const int N=1e9+10;
int q[N],tmp[N],n;void merge_sort(int q[],int l,int r)
{if(l>=r)return;int mid=l+r>>1;merge_sort(q,l,mid),merge_sort(q,mid+1,r);int k=0,i=l,j=mid+1;while(i<=mid&&j<=r)if(q[i]<=q[j])tmp[k++]=q[i++];else tmp[k++]=q[j++];while(i<=mid) tmp[k++]=q[i++];while(j<=r) tmp[k++]=q[j++];for(i=l,j=0;l<=r;i++,j++)q[i]=tmp[j];
}int main(){scanf("%d",&n);for(int i=0;i<n;i++)scanf("%d",&q[i]);merge_sort(q,0,n-1); for(int i=0;i<n;i++)printf("%d",q[i]);return 0;
}