poj3660 Cow Contest的相關內容介紹

poj3660 Cow Contest的相關內容介紹

Cow Contest   Time Limit:1000MS   Memory Limit:65536K Total Submissions:8986   Accepted:5045  

Description

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 cowAhas a greater skill level than cowB(1 ≤A≤N; 1 ≤B≤N;A≠B), then cowAwill always beat cowB.

Farmer John is trying to rank the cows by skill level. Given a list the results ofM(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.

 

Input

* Line 1: Two space-separated integers:NandM
* 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:AandB

 

Output

* Line 1: A single integer representing the number of cows whose ranks can be determined
　

 

Sample Input

5 5
4 3
4 2
3 2
1 2

Sample Output

2

Source

USACO 2008 January Silver  
  題意：n頭牛，給出一部分牛的排名情況，求最後確定排名的牛的頭數。   分析：。。。。坑的一逼，不想說話，我想靜靜。  
 

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