Mergeable Stack 直接list内置函数。(152 - The 18th Zhejiang University Programming Contest Sponsored by TuSimple)

题意：模拟栈，正常pop，push，多一个merge A B 形象地说就是就是将栈B堆到栈A上。

题解：直接用list 的pop_back,push_back,splice 模拟，

坑：用splice，第一次超时，正要大改 发现是cin超时。。。

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<vector>
#include<cstring>
#include<set>
#include<algorithm>
#include<stack>
#include<string>
#include<cstdio>
#include<list>
#define _for(i, a, b) for (int i = (a); i<(b); ++i)
using namespace std;
const int N = 3e5 + ;
const int INF = 1e6;
list<int> v[N];

int main()
{
    int t;
    cin >> t;
    while (t--) {
        int n, q; int a, b;

        cin >> n >> q;
        _for(i, , n + )v[i].clear();
        while (q--) {
            int x;
            scanf("%d", &x);
            if (x == ) {
                scanf("%d%d", &a, &b);
                v[a].push_back(b);
            }
            if (x == ) {
                int b; scanf("%d", &b);
                if (v[b].empty())printf("EMPTY\n");
                else {
                    printf("%d\n", v[b].back());
                    v[b].pop_back();
                }

            }
            if (x == ) {
                scanf("%d%d", &a, &b);
                v[a].splice(v[a].end(), v[b]);
            }
        }
    }
    //system("pause");
    return ;
}