poj3660Cow Contest(Floyd闭包)
2016-01-23 23:35
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题意:给出一些牛的强弱关系,问有多少只牛能确定其排名
思路:把牛看成顶点,A强于B就在A和B连一条边,然后用Floyd跑一遍传递闭包,如果一只牛赢的次数和输的次数加起来等于n-1,那么就可以确定了
吐槽:一开始以为只要某个顶点连入的边数等于n-1就可以了,(怎么会这么简单)后来WA了一次之后发现如果A赢B,B赢C,就算A不和C打也能确定A能赢C
题目
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 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
Sample Output
思路:把牛看成顶点,A强于B就在A和B连一条边,然后用Floyd跑一遍传递闭包,如果一只牛赢的次数和输的次数加起来等于n-1,那么就可以确定了
吐槽:一开始以为只要某个顶点连入的边数等于n-1就可以了,(怎么会这么简单)后来WA了一次之后发现如果A赢B,B赢C,就算A不和C打也能确定A能赢C
#include <cstdio> #include <queue> #include <cstring> #include <iostream> #include <cstdlib> #include <algorithm> #include <vector> #include <map> #include <string> #include <set> #include <ctime> #include <cmath> #include <cctype> using namespace std; #define maxn 505 #define LL long long int cas=1,T; int d[maxn][maxn]; const int INF = 1<<29; int n,m; int main() { scanf("%d%d",&n,&m); for (int i = 0;i<m;i++) { int a,b; scanf("%d%d",&a,&b); d[a][b]=1; } for (int k = 1;k<=n;k++) for (int i = 1;i<=n;i++) for (int j = 1;j<=n;j++) d[i][j]=d[i][j] || (d[i][k] && d[k][j]); int ans = 0; for (int i = 1;i<=n;i++) { int anss = 0; for (int j = 1;j<=n;j++) { anss+=d[i][j]+d[j][i]; } if (anss==n-1) ans++; } printf("%d\n",ans); //freopen("in","r",stdin); //scanf("%d",&T); //printf("time=%.3lf",(double)clock()/CLOCKS_PER_SEC); return 0; }
题目
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 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
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