poj 1363(Stack ) Rails

Rails

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 21050 Accepted: 8404

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

51 2 3 4 55 4 1 2 3066 5 4 3 2 100

Sample Output

YesNoYes题目大意：有n节车厢从A方向驶进车站，按进站顺序编号为1-n.你的任务是让它们按照某种可定的顺序进入B方向的铁轨并驶出车站。可以借助中转站C，该中转站是一个可以停放任意多节车厢的车站，但由于末端封顶，驶入C的车厢必须按照相反的顺序驶出C。对于每个车厢，一旦从A进入C，就不能再回到A了，一旦从C进入B，就不能回到B了（典型的栈结构）。我用的是STL中stack来实现模拟栈的，参考了刘汝佳的书(p93，例题6.1.2），过程再仔细想一想，在草稿纸上画一画。注意输入输入的格式，挺蛋疼的。。
#include <iostream>#include <cstdio>#include <stack>#include <algorithm>#include <cstring>using namespace std;const int maxn=100000;int target[maxn];int main(){    //freopen("in.txt","r",stdin);    int n;    stack<int>s;  while(scanf("%d",&n)!=EOF&&n!=0)    {        memset(target,0,sizeof(target));  //不知道是什么毛病，对于多次输入，我有这种清空的习惯，见谅        while(!s.empty())   s.pop();   //同上        while(1)        {            while(!s.empty())   s.pop(); //不知道有没有必要，我有这种习惯。。            int i,ok=1,is_zero=0;            for(i=1;i<=n;i++)            {                scanf("%d",&target[i]);                if(i==1&&!target[i])                {                  is_zero=1;   //看输入火车的第一个数是否为0,如果为0，就退出，输入下一个n                  break;                }            }            if(is_zero)                break;   //输入火车序号的第一个数为0，退出，输入下一个n            int A=1,B=1;            while(B<=n)            {                if(A==target[B])                    A++,B++;                else if(!s.empty()&&s.top()==target[B])                    s.pop(),B++;                else if(A<=n)                    s.push(A++);                else                {                    ok=0;                    break;                }            }            if(ok)printf("Yes\n");            elseprintf("No\n");        }        printf("\n");    }    return 0;}