题目链接：走你

题目大意，给定一个初始字符串和一个目标串，令初始串以不同的入栈、出栈顺序构造目标串，输出所有方案。

大暴力

暴力出奇迹嘛，到了初始串的第i个位置，只有两种选择，入栈和出栈，故直接深搜枚举入栈出栈顺序(然而老年人连DFS都快不会写了)

code

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

vector <char> ans;
int len;
stack <char> sta;
string a, b;

void DFS (int in, int out) {
    if (in == len && out == in) {
        for (int i = 0;i < 2 * len; ++ i) {
            cout << ans[i] << ' ';
        }
        cout << endl;
        return;
    }
    if (in + 1 <= len) {
        sta.push (a[in]);
        ans.push_back ('i');
        DFS (in + 1, out);
        sta.pop ();
        ans.pop_back ();
    }

    if (out < in && out + 1 <= len && sta.top () == b[out]) {
        char t = sta.top ();
        sta.pop ();
        ans.push_back ('o');
        DFS (in, out + 1);
        sta.push (t);
        ans.pop_back ();
    }
}

int main () {
    while (cin >> a >> b) {
        ans.clear ();
        len = a.size ();
        cout << "[" << endl;
        DFS (0, 0);
        cout << "]" << endl;
    }
    return 0;
}