poj 1363 Rails (【栈的应用】 刘汝佳的写法 *学习)

Rails

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 25964		Accepted: 10199

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

代码：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <algorithm>
#include <stack>

using namespace std;

int main()
{
    int n;
    int i, j;
    int a[1010];
    stack<int>q;

    while(scanf("%d", &n) && n!=0 )
    {
        while(scanf("%d", &a[0]) && a[0]!=0 )
        {
            for(i=1; i<n; i++)
            {
                scanf("%d", &a[i] );
            }
            int A=1, B=0;
            int flag=1;
            while(!q.empty())
            {
                q.pop();
            }
            while( B<n )
            {
                if(A==a[B])
                {
                    A++; B++;
                }
                else if(!q.empty() && q.top()==a[B] )
                {
                    q.pop(); B++;
                }
                else if(A<=n)
                    q.push(A++);
                else
                {
                    flag=0; break;
                }
            }
            printf("%s\n", flag==1?"Yes":"No" );
        }
        printf("\n");
    }
    return 0;
}