poj1094——Sorting It All Out（拓扑排序）
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.
题意是给出一些比较关系，求给出这些关系的过程中1 ）能否有一个确定的排序，有的话给出关系的个数并求出这个排序的序列；2）是否成环；3）不能确定
只有一个确定排序的拓扑序列的性质应该是，只有一个入度为0的节点，去掉此节点后，剩下的还是只有一个入度为0的点。按照这个性质模拟就行了。
#include printf("%c",q[j]+'A'-1);
printf(".\n");
flag=1;
}
}
if(!flag)
printf("Sorted sequence cannot be determined.\n");
}
return 0;
}