poj 3660 Cow Contest
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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 cow A has a greater skill level than cow B (1 ≤ A ≤ N; 1 ≤ B ≤ N; A ≠ B), then cowA 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 54 34 23 21 22 5
Sample Output
2
思路:先判断是否联通 然后分别统计个点的入度和出度之和靠是否为n-1 即可 传递闭包的性质出度和入度和为n-1的时候其顺序是唯一确定的
#include <iostream>#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>#include <stack>#include <queue>#include <set>#include <vector>using namespace std;#define maxn 105#define INF 1000000000int d[maxn][maxn];int n,m; void floyd(){int i,j,k;for(i=1;i<=n;i++){for(j=1;j<=n;j++){for(k=1;k<=n;k++){//if(d[j][i]!=-1&&d[i][k]!=-1)//if(d[j][k]==-1)d[j][k]=d[j][k]||(d[j][i]&&d[i][k]);}}}}int main(){int i,j;int a,b;scanf("%d %d",&n,&m); memset(d,0,sizeof(d)); for(i=0;i<m;i++){ scanf("%d %d",&a,&b); d[a][b]=1;}floyd();int cnt=0,k=0;for(i=1;i<=n;i++){ k=0;for(j=1;j<=n;j++){ if(d[i][j]||d[j][i]) k++; }if(k==n-1)cnt++;}cout<<cnt<<endl;return 0;}
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