http://poj.org/problem?id=3660
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.
Input
* 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
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 2 5
Sample Output
2
题解：$floyd$ 算法 如果赢过的人加上败给的人的和是 $N - 1$ 就是可以确定位置的人
代码：
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <math.h>
using namespace std;
int N, M;
int mp[110][110];
void floyd() {
for(int k = 1; k <= N; k ++) {
for(int i = 1; i <= N; i ++) {
if(mp[i][k])
for(int j = 1; j <= N; j ++) {
if(mp[k][j] == 1 && mp[i][k] == 1) {
mp[i][j] = 1;
mp[j][i] = -1;
}
else if(mp[k][j] == -1 && mp[i][k] == -1) {
mp[i][j] = -1;
mp[j][i] = 1;
}
else continue;
}
}
}
}
int main() {
memset(mp, 0, sizeof(mp));
scanf("%d%d", &N, &M);
for(int i = 1; i <= M; i ++) {
int a, b;
scanf("%d%d", &a, &b);
mp[a][b] = 1;
mp[b][a] = -1;
}
floyd();
int ans = 0;
for(int i = 1; i <= N; i ++) {
int sum = 0;
for(int j = 1; j <= N; j ++)
if(mp[i][j])
sum ++;
if(sum == N - 1)
ans ++;
}
printf("%d\n", ans);
return 0;
}
原文地址：https://www.cnblogs.com/zlrrrr/p/9895713.html