POJ1363Rails队列和栈应用

题目

POJ-1363 Rails
Description

There is a famous railway station in PopPush City. Country there is incredibly hilly. The station was built in last century. Unfortunately, funds were extremely limited that time. It was possible to establish only a surface track. Moreover, it turned out that the station could be only a dead-end one (see picture) and due to lack of available space it could have only one track.

The local tradition is that every train arriving from the direction A continues in the direction B with coaches reorganized in some way. Assume that the train arriving from the direction A has N <= 1000 coaches numbered in increasing order 1, 2, …, N. The chief for train reorganizations must know whether it is possible to marshal coaches continuing in the direction B so that their order will be a1, a2, …, aN. Help him and write a program that decides whether it is possible to get the required order of coaches. You can assume that single coaches can be disconnected from the train before they enter the station and that they can move themselves until they are on the track in the direction B. You can also suppose that at any time there can be located as many coaches as necessary in the station. But once a coach has entered the station it cannot return to the track in the direction A and also once it has left the station in the direction B it cannot return back to the station.

Input

The input consists of blocks of lines. Each block except the last describes one train and possibly more requirements for its reorganization. In the first line of the block there is the integer N described above. In each of the next lines of the block there is a permutation of 1, 2, …, N. The last line of the block contains just 0.

The last block consists of just one line containing 0.
Output

The output contains the lines corresponding to the lines with permutations in the input. A line of the output contains Yes if it is possible to marshal the coaches in the order required on the corresponding line of the input. Otherwise it contains No. In addition, there is one empty line after the lines corresponding to one block of the input. There is no line in the output corresponding to the last ``null’’ block of the input.
Sample Input

5
1 2 3 4 5
5 4 1 2 3
0
6
6 5 4 3 2 1
0
0
Sample Output

Yes
No

Yes

题目翻译

有数字序列1，2，…n这样严格顺序入栈。由于进栈出栈时间不同，所以有很多合法的组合。只有符合栈的规则的，即后进先出的才是合法的。

下面举例说明不合法:1,2,3按照顺序入栈，如果出现1，2这样的出栈即是不合法。因为1，2 不满足后进先出的规则，应该是2在前1再后出栈。

解题思路

采用队列queue和栈stack组合使用。

队列queue保存待判断的序列，比如样例中的5 4 1 2 3
1,2，，，n按照顺序进栈stack，判断栈顶元素top()是否等于队首元素front(),如果相等，则说明有合法的可能性，同时弹出队首元素和栈顶元素
最后如果栈空，则说明待判断的序列是合法的序列。

代码说明:
这里的函数参数为队列，需要传进来一个队列。看似多此一举，实则锻炼自己形参形式的转化能力。
是不是还没用过队列queue作为函数的形参呢？

代码

#include<iostream>
#include<queue>
#include<stack>using namespace std;bool check(queue<int> &order)
{stack<int> S;int n=order.size();//长度for(int i=0;i<n;++i){S.push(i+1);//入栈while(!S.empty()&&order.front()==S.top())//队首==栈顶{order.pop();//同时弹出S.pop();}} if(!S.empty())return false;return true;  //栈为空，说明合法
}int main()
{queue<int> Q;int T,temp1,temp,a[10000];while(1){cin>>T;//读入位数if(T==0) break;while(1){cin>>a[0];//读入一行数据if(a[0]==0) break; //第一个数据为零，则退出到上层whileQ.push(a[0]);for(int i=1;i<T;++i){cin>>a[i];//借助数组，进入队列Q.push(a[i]);}if(check(Q))//调用判断合法函数cout<<"Yes"<<endl;elsecout<<"No"<<endl;while(!Q.empty())//清空队列Q.pop();}cout<<endl;//输出空行，跟位数T是一组。}return 0;
}

总结：
该题考查基本的栈的应用。
该题需要注意输入输出的格式。

5
1 2 3 4 5
5 4 1 2 3
0
6
6 5 4 3 2 1
0
0

这样的输入该怎么处理呢？

可以看出这里结束录入的条件是输入0 回车 0 回车。即：

0
0

同时还要求是同一位数n的数据输出结束后，输出一个空行。

while（1）
{cin>>n;//位数if(n==0) break;//退出该层循环//下面读入每一行数据，这时候要考虑开头为0，则为结束的标志。while(1){cin>>a[0];if(a[0]==0) break;for(int i=1;i<n;++i)cin<<a[i];}
cout<<endl;//这里和位数n并列
}

希望本次总结对你有帮助。