AcWing 787. 归并排序

#include <iostream>
using namespace std;

const int N = 1e6 + 10;

int n;
int q[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 i = l, j = mid + 1, k = 0;
    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 (int i = l, j = 0; i <= r; ++ i, ++ j)  q[i] = tmp[j];
    
    return ;
}

int main()
{
    cin >> n;
    
    for (int i = 0; i < n; ++ i)    cin >> q[i];
    
    merge_sort(q, 0, n - 1);
    
    for (int i = 0; i < n; ++ i)    cout << q[i] << " ";
    
    return 0;
}