[STL][list]Mergeable Stack

Mergeable Stack

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Time Limit: 2 Seconds      Memory Limit: 65536 KB

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Given initially empty stacks, there are three types of operations:

• 1 s v: Push the value onto the top of the -th stack.

• 2 s: Pop the topmost value out of the -th stack, and print that value. If the -th stack is empty, pop nothing and print "EMPTY" (without quotes) instead.

• 3 s t: Move every element in the -th stack onto the top of the -th stack in order.

  Precisely speaking, denote the original size of the -th stack by , and the original size of the -th stack by . Denote the original elements in the -th stack from bottom to top by , and the original elements in the -th stack from bottom to top by .

  After this operation, the -th stack is emptied, and the elements in the -th stack from bottom to top becomes . Of course, if , this operation actually does nothing.

There are operations in total. Please finish these operations in the input order and print the answer for every operation of the second type.

Input

There are multiple test cases. The first line of the input contains an integer , indicating the number of test cases. For each test case:

The first line contains two integers and ( ), indicating the number of stacks and the number of operations.

The first integer of the following lines will be ( ), indicating the type of operation.

• If , two integers and ( , ) follow, indicating an operation of the first type.
• If , one integer ( ) follows, indicating an operation of the second type.
• If , two integers and ( , ) follow, indicating an operation of the third type.

It's guaranteed that neither the sum of nor the sum of over all test cases will exceed .

Output

For each operation of the second type output one line, indicating the answer.

Sample Input

2
2 15
1 1 10
1 1 11
1 2 12
1 2 13
3 1 2
1 2 14
2 1
2 1
2 1
2 1
2 1
3 2 1
2 2
2 2
2 2
3 7
3 1 2
3 1 3
3 2 1
2 1
2 2
2 3
2 3

Sample Output

13
12
11
10
EMPTY
14
EMPTY
EMPTY
EMPTY
EMPTY
EMPTY
EMPTY

思路：用链表结构来模拟栈的增加、删除元素，合并栈的操作。可以手写链表结构或直接使用STL里的list

下面总结一些常用的list的用法：

//定义list容器a
list<int > a;//定义一个元素为int型的list
list<int > a(n);//定义一个有n个元素且元素为int型的list，每个元素都是0
list<int > a(n,m);//同上，不过每个元素都是m

//基本操作
a.clear();//清空list中的所有元素
a.empty();//判断list是否为空
a.front();//获得list的头部元素
a.back();//获得list的最后一个元素
a.push_front();//从list的头部插入元素
a.push_back();//从list的末端插入元素
a.pop_front();//删掉头部第一个元素
a.pop_back();//删掉尾部第一个元素
a.splice(a.begin(),b);//将链表b插入到链表a的链头
a.splice(a.end(),b);//将链表b插入到链表a的链尾

AC代码：

#include <iostream>
#include<cstdio>
#include<list>
using namespace std;

list<int> a[300010];

int main()
{
    int t;
    scanf("%d",&t);
    while(t--){
        int n,q;
        scanf("%d%d",&n,&q);
        for(int i=0;i<300010;i++) a[i].clear();
        while(q--){
            int op;
            scanf("%d",&op);
            if(op==1){
                int stk,x;
                scanf("%d%d",&stk,&x);
                a[stk].push_back(x);
            }
            if(op==2){
                int stk;
                scanf("%d",&stk);
                if(!a[stk].empty()) {
                    printf("%d
",a[stk].back());
                    a[stk].pop_back();
                }
                else printf("EMPTY
");
            }
            if(op==3){
                int stk1,stk2;
                scanf("%d%d",&stk1,&stk2);
                a[stk1].splice(a[stk1].end(),a[stk2]);
            }
        }
    }
    return 0;
}