模拟,dfs

#include <iostream>
#include <vector>
#include <stack>

using namespace std;

int n, cnt = 20;
vector<int> state1;
stack<int> state2;
int state3 = 1;

void dfs()
{
    if(!cnt) return;
    if(state1.size() == n)
    {
        cnt--;
        for(auto x : state1) cout<<x;
        cout<<endl;
        return;
    }

    if(state2.size())
    {
        state1.push_back(state2.top());
        state2.pop();
        dfs();
        // 恢复现场
        state2.push(state1.back());
        state1.pop_back();
    }

    if(state3<=n)
    {
        state2.push(state3);
        state3 ++;
        dfs();
        state3 --;
        state2.pop();
    }
}

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

解法二

参考

#include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
#include <queue>
using namespace std;

int n;
vector<int> a;
// 判断出栈顺序是否合法
bool check()
{
    stack<int> s;
    queue<int> q;
    for(int i = 0; i < n; i++) q.push(a[i]);
    for(int i = 1; i <= n; i++)
    {
        s.push(i);
        while(!s.empty() && s.top()==q.front()) s.pop(), q.pop();
    }
    if(s.size()==0) return true;
    else return false;
}
int main()
{
    cin >> n;
    for(int i = 1; i <= n; i++)
        a.push_back(i);
    int cnt = 0;
    do
    {
        if(check())
        {
            for(int i = 0; i < n; i++) cout << a[i];
            cout << endl;
            cnt++;
            if(cnt==20) break;
        }
    }while(next_permutation(a.begin(), a.end()));
    return 0;
}

作者：虹之间
链接：https://www.acwing.com/solution/acwing/content/7484/
来源：AcWing
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