Poj/OpenJudge 1094 Sorting It All Out

1.链接地址：

http://poj.org/problem?id=1094

http://bailian.openjudge.cn/practice/1094

2.题目：

Sorting It All Out

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 25547		Accepted: 8861

Description

An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from smallest to largest. For example, the sorted sequence A, B, C, D implies that A < B, B < C and C < D. in this problem, we will give you a set of relations of the form A < B and ask you to determine whether a sorted order has been specified or not.

Input

Input consists of multiple problem instances. Each instance starts with a line containing two positive integers n and m. the first value indicated the number of objects to sort, where 2 <= n <= 26. The objects to be sorted will be the first n characters of the uppercase alphabet. The second value m indicates the number of relations of the form A < B which will be given in this problem instance. Next will be m lines, each containing one such relation consisting of three characters: an uppercase letter, the character "<" and a second uppercase letter. No letter will be outside the range of the first n letters of the alphabet. Values of n = m = 0 indicate end of input.

Output

For each problem instance, output consists of one line. This line should be one of the following three:

Sorted sequence determined after xxx relations: yyy...y.
Sorted sequence cannot be determined.
Inconsistency found after xxx relations.

where xxx is the number of relations processed at the time either a sorted sequence is determined or an inconsistency is found, whichever comes first, and yyy...y is the sorted, ascending sequence.

Sample Input

4 6
A<B
A<C
B<C
C<D
B<D
A<B
3 2
A<B
B<A
26 1
A<Z
0 0

Sample Output

Sorted sequence determined after 4 relations: ABCD.
Inconsistency found after 2 relations.
Sorted sequence cannot be determined.

Source

East Central North America 2001

3.思路：

 

4.代码：

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>

using namespace std;

int n,m;
int map[30][30];
int reg[100];
int in[30],out[30];
char ans[30];
int stack[30];
void fun()
{
     int i,j;
     for(i='A',j=1;i<='Z';i++,j++)reg[i]=j;
}
void toposort(char *ans)
{
    int i,top=0,u,s=0;
    for(i=1;i<=n;i++)
     if(in[i]==0)stack[top++]=i;
    while(top!=0)
    {
       u=stack[--top];
       ans[s++]=u+64;
       for(i=1;i<=n;i++)
       {
         if(map[u][i])
         {
            in[i]--;
            if(!in[i])stack[top++]=i;
         }
       }
    }
    ans[s]=0;
}
int main()
{
    int i,j,x,y,k,flag1,flag2,flag;
    fun();
    char ch[5];
    while(1)
    {
      flag1=flag2=0;
      memset(map,0,sizeof(map));
      scanf("%d%d",&n,&m);
      if(n==0&&m==0)break;
      for(i=1;i<=m;i++)
      {
         flag=1;
         scanf("%s",ch);
         x=reg[ch[0]];
         y=reg[ch[2]];
         map[x][y]=1;
         if(x==y)flag1=i;
         memset(in,0,sizeof(in));
         memset(out,0,sizeof(out));
         if(!flag1&&!flag2)
         for(j=1;j<=n;j++)
          for(k=1;k<=n;k++)
          {
             if(j!=x&&k!=y)map[j][k]=map[j][k]||(map[j][x]&&map[y][k]);
             if(j==x&&k!=y)map[j][k]=map[j][k]||map[y][k];
             if(j!=x&&k==y)map[j][k]=map[j][k]||map[j][x];
             if(map[j][k])
             {
               out[j]++;
               in[k]++;
             }
          }
         j=1;
         if(!flag1)
         for(j=1;j<=n;j++)
         {
           if(map[j][j])flag1=i;
           if(in[j]+out[j]!=n-1)flag=0;
         }
         if(flag&&!flag2&&j>n){flag2=i;toposort(ans);}
      }
      if(flag2)
      {
         printf("Sorted sequence determined after %d relations: %s.\n",flag2,ans);
         continue;
      }
      if(flag1)
      {
         printf("Inconsistency found after %d relations.\n",flag1);
         continue;
      }
      printf("Sorted sequence cannot be determined.\n");
    }
    return 0;
}