归并排序c++

#include<iostream>
using namespace std;
#define N 100010
int a[N],tmp[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;i<=r;i++,j++) q[i]=tmp[j];
}
int main(){
    int n,i=0;
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%d",&a[i]);
    }
    merge_sort(a,0,n-1);
    for(i=0;i<n;i++){
        printf("%d ",a[i]);
    }
    return 0;
}