归并排序C++实现

#include<iostream>
using namespace std;
const int maxn  = 100005;
int tmp[maxn];
void mergesort(int a[],int l,int r){
    if(l >= r ) return ;//1wei不需要排
    int mid =l + r >>1;//取中间值
    mergesort(a,l,mid);//左分区
    mergesort(a,mid+1,r);//右分区
    int k = 0, i = l, j = mid + 1;//i和j 做两个指针 左右分区同时比较，小值插入到数组tmp中
    while(i <= mid && j<=r){
        if(a[i] < a[j]) tmp[k++] = a[i++];
        else tmp[k++] = a[j++];
    }
    while(i <= mid) tmp[k++] = a[i++];//处理左分区剩余数据，依次插入tmp
    while(j <= r) tmp[k++] = a[j++];//处理右分区剩余数据，依次插入tmp
    for(int i = l,j = 0;i<=r;i++,j++){
        a[i] = tmp[j];//a依次接收temp数组中的值，存回a数组
    }
}

int main(){
    int n;
    cin>>n;
    int *a = new int[n];
    for(int i =0 ;i<n;i++){
        cin>>a[i];
    }
    mergesort(a,0,n-1);
    for(int i =0;i< n ;i++)
    {
        cout<<a[i];
    }
    return 0;
}