基础算法--归并排序

#include<iostream>
using namespace std;
const int N=1000010;
int a[N],q[N];
void merge_sort(int a[], int l, int r){
    if(l>=r)return ;
    int mid=l+r>>1;
    merge_sort(a,l,mid),merge_sort(a,mid+1,r);
    int i=l,j=mid+1,k=0;
    while(i<=mid&&j<=r){
        if(a[i]<a[j])q[k++]=a[i++];
        else q[k++]=a[j++];
    }
    while(i<=mid)q[k++]=a[i++];
    while(j<=r)q[k++]=a[j++];
    for(i=l,j=0;i<=r;i++,j++)a[i]=q[j];
}
int main(void){
    int n;
    cin>>n;
    for(int i=0;i<n;i++)cin>>a[i];
    merge_sort(a,0,n-1);
    for(int i=0;i<n;i++)cout<<a[i]<<' ';
    return 0;
}