30 人解决，43 人已尝试。
39 份提交通过，共有 74 份提交。
4.2 EMB 奖励。
单点时限: 2.0 sec
内存限制: 256 MB
N (1 <= N <= 100) cows, conveniently numbered 1..N, are participating in a programming contest. As we all know, some cows code better than others. Each cow has a certain constant skill rating that is unique among the competitors.
The contest is conducted in several head-to-head rounds, each between two cows. If cow A has a greater skill level than cow B (1 <= A <=N; 1 <= B <= N; A != B), then cow A will always beat cow B.
Farmer John is trying to rank the cows by skill level. Given a list the results of M (1 <= M <= 4,500) two-cow rounds, determine the number of cows whose ranks can be precisely determined from the results. It is guaranteed that the results of the rounds will not
be contradictory.
Line 1: Two space-separated integers: N and M
Lines 2..M+1: Each line contains two space-separated integers that describe the competitors and results (the first integer, A, is the winner) of a single round of competition: A and B
5 5 4 3 4 2 3 2 1 2 2 5
2 OUTPUT DETAILS: Cow 2 loses to cows 1, 3, and 4. Thus, cow 2 is no better than any of the cows 1, 3, and 4. Cow 5 loses to cow 2, so cow 2 is better than cow 5. Thus, cow 2 must be fourth, and cow 5 must be fifth.The ranks of the other cows cannot be determined.