poj 1094--Sorting It All Out

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.

这题太搞人了- -、给你一定的关系，问你是否出现环或是不唯一的情况，如果不出现的话，序列应该是多少。。
如果是这样的话还不是很烦，可是它加上让你输出第几步的时候出现了这个情况- -。。无语啊。。这也得就每次
输入的时候都得topo一下。当时想的有些混乱了。不过写出来感觉还好- -。。

#include <cstdio>
#include <cstring>
#include <queue>
#include <stack>
#include <algorithm>
using namespace std;
int map[30][30],degree[30];
int rank[30],in[30];
int n,m,cnt;
int flag;//flag标记环，唯一性
void Topo()
{
    int i,j,num,x;
    cnt=flag=0;
    memcpy(in,degree,sizeof(degree));
    for(i=0;i<n;i++)
    {
        num=0;
        for(j=0;j<n;j++)
            if(in[j]==0)
            {
                num++;
                x=j;
            }
        if(num==0)
        {
            flag=1;//有环
            return ;
        }
        if(num>1)
            flag=2;//不唯一
        in[x]--;
        rank[cnt++]=x;
        for(j=0;j<n;j++)
            if(map[x][j])
                in[j]--;
    }
}
int main()
{
    char s[5];
    int i,j;
    while(scanf("%d%d",&n,&m)&&(n+m))
    {
        memset(degree,0,sizeof(degree));
        memset(map,0,sizeof(map));
        flag=2;
        for(i=1;i<=m;i++)
        {
            scanf("%s",s);
            map[s[0]-'A'][s[2]-'A']=1;
            degree[s[2]-'A']++;
            if(flag==2)
               Topo();
            if(flag==1)
            {
                printf("Inconsistency found after %d relations.\n",i);
        flag=3;
            }
            else if(!flag)
            {
                printf("Sorted sequence determined after %d relations: ",i);
                for(j=0;j<n;j++)
                    printf("%c",rank[j]+'A');
                printf(".\n");
        flag=3;
            }
        }
        if(flag==2)
            printf("Sorted sequence cannot be determined.\n");
    }
    return 0;
}