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[][];
 int reg[];
 int in[],out[];
 char ans[];
 int stack[];
 void fun()
 {
      int i,j;
      for(i='A',j=;i<='Z';i++,j++)reg[i]=j;
 }
 void toposort(char *ans)
 {
     int i,top=,u,s=;
     for(i=;i<=n;i++)
      if(in[i]==)stack[top++]=i;
     while(top!=)
     {
        u=stack[--top];
        ans[s++]=u+;
        for(i=;i<=n;i++)
        {
          if(map[u][i])
          {
             in[i]--;
             if(!in[i])stack[top++]=i;
          }
        }
     }
     ans[s]=;
 }
 int main()
 {
     int i,j,x,y,k,flag1,flag2,flag;
     fun();
     char ch[];
     while()
     {
       flag1=flag2=;
       memset(map,,sizeof(map));
       scanf("%d%d",&n,&m);
       if(n==&&m==)break;
       for(i=;i<=m;i++)
       {
          flag=;
          scanf("%s",ch);
          x=reg[ch[]];
          y=reg[ch[]];
          map[x][y]=;
          if(x==y)flag1=i;
          memset(in,,sizeof(in));
          memset(out,,sizeof(out));
          if(!flag1&&!flag2)
          for(j=;j<=n;j++)
           for(k=;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=;
          if(!flag1)
          for(j=;j<=n;j++)
          {
            if(map[j][j])flag1=i;
            if(in[j]+out[j]!=n-)flag=;
          }
          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 ;
 }