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.

题意是问是否存在唯一的序列，如果不存在，要么是不唯一，要么是直接不存在，也就是存在环，拓扑排序，每次读入都进行一次排序，然后通过返回值判断。

代码：
#include <iostream>
#include <map>
#include <queue>
#include <cmath>
#include <cstdio>
#include <algorithm>
#include <cstring>
#define inf 10001
using namespace std;
int n,m;
int mp[26][26];///记录两个点是否存在前后顺序
int ok[26],unsure;///ok记录某个点前面是否有点 unsure记录顺序是否唯一
char ans[27],x,y,ch;///ans记录唯一的序列 index为下标 flag记录第几步中断
int index,flag;
int topsort()///拓扑
{
    queue<int> q;
    unsure = 0;///初始
    index = 0;///初始
    int vis[26] = {0};///当vis的值和ok相同就相当于这个点前面已经没有点了，可以进入ans序列
    for(int i = 0;i < n;i ++)
    {
        if(vis[i] == ok[i])q.push(i);
    }
    if(q.empty())return -1;///如果不存在这样的点 说明存在环
    while(!q.empty())
    {
        if(q.size() > 1)
        {
            unsure = 1;///存在多个点无前后确定关系
        }
        ans[index ++] = q.front() + 'A';///进入ans序列
        for(int i = 0;i < n;i ++)
        {
            if(mp[q.front()][i])
            {
                vis[i] ++;///i前面的点少了一个 之所以用vis，是维护ok和mp数组不变保证每次都是完整的拓扑
                if(vis[i] == ok[i])q.push(i);
                else if(vis[i] > ok[i])return -1;//有环
            }
        }
        q.pop();
    }
    return 1;
}
int main()
{
    while(cin>>n>>m&&(n + m))
    {
        index = 0;
        flag = -1;
        int d = 0;
        memset(mp,0,sizeof(mp));
        memset(ok,0,sizeof(ok));
        for(int i = 0;i < m;i ++)
        {
            cin>>x>>ch>>y;
            if(!mp[x - 'A'][y - 'A'])
            {
                if(ch == '<')
                {
                    mp[x - 'A'][y - 'A'] = 1;
                    ok[y - 'A'] ++;
                }
                else if(ch == '>')
                {
                    mp[y - 'A'][x - 'A'] = 1;
                    ok[x - 'A'] ++;
                }
            }
            if(d == 1 || d == -1)continue;
            d = topsort();
            if(d == 1)///排序进行完
            {
                if(index == n)///n个点排好序了
                {
                    if(unsure == 0)flag = i + 1,ans[index] = '\0';///序列唯一
                    else d = 0;//不唯一
                }
                else///有环
                {
                    d = -1,flag = i + 1;
                }
            }
            else if(d == -1)flag = i + 1;///有环
        }
        if(!d)printf("Sorted sequence cannot be determined.\n");
        else if(d == 1)printf("Sorted sequence determined after %d relations: %s.\n",flag,ans);
        else printf("Inconsistency found after %d relations.\n",flag);
    }
}