难难难

#include <iostream>
using namespace std;

const int N = 10;
int n;

void dfs(int u, int nums[], bool st[])
{
    if(u > n) 
    {
        for (int i = 1; i <= n; i ++) cout << nums[i] <<' ';
        cout << endl;
    }    
    else
    {
        for (int i = 1; i <= n; i ++)
        {
            if(!st[i])
            {
                st[i] = true;
                nums[u] = i;
                dfs(u + 1, nums, st);
                st[i] = false;//恢复现场
            }
        }
    }

}

int main()
{
    cin >> n;
    int nums[N];
    bool st[N] = {0};
    dfs(1, nums, st);
    return 0;

}