题解 | #火车进站#

todo : 增加说明

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

void dfs(const vector<int>& in, int index, stack<int>& st, vector<int>& out, vector<vector<int>>& res)
{
    if (index >= in.size() && st.empty()) {
        res.push_back(out);
        return;
    }
    // 进
    if (index < in.size()) {
        st.push(in[index]);
        dfs(in, index + 1, st, out, res);
        st.pop();
    }
    // 出
    if (!st.empty()) {
        out.push_back(st.top());
        st.pop();
        dfs(in, index, st, out, res);
        st.push(out.back());
        out.pop_back();
    }
}

int main()
{
    int n;
    while (cin >> n) {
        vector<int> nums(n);
        for (int i = 0; i < n; ++i) { cin >> nums[i]; }
        stack<int> st;
        vector<int> path;
        vector<vector<int>> res;
        dfs(nums, 0, st, path, res);
        sort(res.begin(), res.end());
        for (auto p : res) {
            for (int a : p) { cout << a << " "; }
            cout << endl;
        }
    }
    return 0;
}