C++ 代码

#include <iostream>
#include <vector>
#include <stack>
using namespace std;
int n, cnt = 1;
stack<int> s;
vector<int> v;

void dfs(int idx){
    if(cnt > 20) return;
    if(v.size() == n){
        ++ cnt;
        for(int i : v)  cout << i;
        cout << endl;
        return;
    }

    if(s.size()){ //先出栈，这样字典序小
        v.push_back(s.top());
        s.pop();
        dfs(idx);
        s.push(v.back());
        v.pop_back();
    }

    if(idx <= n){ //压栈
        s.push(idx);
        dfs(idx + 1);
        s.pop();
    }
}

int main()
{
    cin >> n;
    dfs(1);
    return 0;
}