SGU 271 - Book Pile

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#栈 #双向队列 #string

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本文介绍了一个关于书堆操作的问题，包括向书堆顶部添加书籍和将顶部书籍逆序的操作，并提供了一种使用双向队列和栈来高效解决该问题的方法。

271. Book Pile

time limit per test: 0.25 sec.
memory limit per test: 65536 KB

input: standard
output: standard

There is a pile of N books on the table. Two types of operations are performed over this pile:
- a book is added to the top of the pile,
- top K books are rotated. If there are less than K books on the table, the whole pile is rotated.
First operation is denoted as ADD(S) where S is the name of the book, and the second operations is denoted as ROTATE.
The maximum number of books is no more than 40000. All book names are non-empty sequences of no more than 3 capital Latin letters. The names of the books can be non-unique.

Input

The first line of input file contains 3 integer numbers N, M, K (0 <= N <= 40000; 0 <= M <= 100000; 0 <= K <= 40000). The following N lines are the names of the books in the pile before performing any operations. The book names are given in order from top book to bottom. Each of the following M lines contains the operation description.

Output

Output the sequence of books names in the pile after performing all operations. First line corresponds to the top book.

Sample test(s)

Input

2 3 2

ADD(C)

ROTATE

ADD(D)

Output

D
A
C
B

==============================

简单翻译一下：

桌子上有一摞书n本，对于这摞书有两种操作：

1、添加一本书到最上面 ADD(书名s)

2、使最上面k本书逆序，如果总数小于k则所有书逆序 ROTATE

书本数最大不超过40000，书名是不超过三个的大写字母，书名不是唯一的（可能有重名的）

输入n m和k，桌子上的n本书从上到下，m个操作

书从上到下输出结果

学会了双向队列deque，和普通队列差别不大很容易。

始终保持队列中元素小于等于k，因为每次只需要对前k本书进行操作，也就是后面的书永远都不会被操作，可以直接加入栈ans。ROTATE的时候用一个标记表示双向队列的头是顶端或者尾是顶端即可。

string中c_str()函数使string转化为char可以用printf输出

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <stack>
#include <queue>
using namespace std;

deque<string>que;
stack<string>ans;

int main()
{
    int n,m,k,flag=true;
    char a[5],str[20];
    scanf("%d%d%d",&n,&m,&k);
    for(int i=0;i<n;i++)
    {
        scanf("%s",a);
        que.push_back(a);
    }
    while(que.size()>k)
    {
        ans.push(que.back());
        que.pop_back();
    }
    for(int i=0;i<m;i++)
    {
        scanf("%s",str);
        if(str[0]=='A')
        {
            int len=strlen(str);
            int sz=0;
            for(int i=4;i<len-1;i++) a[sz++]=str[i];
            a[sz]=0;
            //cout<<"a="<<a<<endl;
            if(flag) que.push_front(a);
            else que.push_back(a);
            if(que.size()>k&&flag)
            {
                ans.push(que.back());
                que.pop_back();
            }
            else if(que.size()>k&&!flag)
            {
                ans.push(que.front());
                que.pop_front();
            }
        }
        else
        {
            flag=!flag;
            //cout<<"size="<<que.size()<<endl;
        }
    }
    if(flag)
    {
        while(!que.empty())
        {
            ans.push(que.back());
            que.pop_back();
        }
    }
    else
    {
        while(!que.empty())
        {
            ans.push(que.front());
            que.pop_front();
        }
    }
    while(!ans.empty())
    {
        printf("%s\n",ans.top().c_str());
        //cout<<ans.top()<<endl;
        ans.pop();
    }
    return 0;
}