uva: Cow Contest ( Floyd Warshall – Transitive Closure)

Cow Contest


Problem :

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.


The input contains multiple test cases, until the end of file. Each test case is given in the following order:

  • 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


For each test case, output in a single line, a single integer representing the number of cows whose ranks can be determined.



Solution analysis:


 C++ Solution:

#include <stdio.h>
#define NMAX 100

int beating[NMAX+1][NMAX+1];

int main()
	int m,n,i,j,k,result;

	while(EOF != scanf("%d %d", &n, &m))

		for(i=0; i < n; i++)
			for(j=0; j < n; j++)
				beating[i][j] = 0;
			beating[i][i] = 1;

			scanf("%d %d",&i,&j);
			beating[--i][--j] = 1;

	for(k=0; k < n; k++)
		for(i=0; i< n; i++)
			for(j=0; j < n; j++)
				if( beating[i][k] &&  beating[k][j] )
					beating[i][j] = 1;

	result = 0;
	for(i=0;i < n ; i++)
		int nReachable=0;

		for(j=0; j < n; j++)
			nReachable+= beating[i][j] + beating[j][i];

		if(nReachable == n+1 ) result++;

		printf("%d\n", result);

	return 0;



Sample Input

5 5
4 3
4 2
3 2
1 2
2 5

Sample Output



About M Moniruzzaman
A passionate software engineer, have been developing applications on various platforms such as Android, iPhone, .Net (C#) technologies and web based ASP.NET, PHP, JavaScript, jQuery technologies for more than 10 years. Especially I have expertise on developing applications for Android and iPhone, as well as service oriented, client-server based applications where clients will be reside on Android/iPhone that communicate with WCF(.NET) service hosted on server. I have completed certification in Microsoft Certified Professional Developer (MCPD) on .Net 4 . I have completed my graduation in -- B.Sc. (Engineering) in Computer Science and Engineering, ShahJalal University of Science and Technology, Bangladesh. Thanks, M. Moniruzzaman (Zaman)

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