HDU 4324:Triangle LOVE( 拓扑排序 )
2017-06-01 14:12
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Triangle LOVE
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/65536 K (Java/Others)Total Submission(s): 2271 Accepted Submission(s): 946
[align=left]Problem Description[/align]
Recently, scientists find that there is love between any of two people. For example, between A and B, if A don’t love B, then B must love A, vice versa. And there is no possibility that two people love each other, what a crazy world!
Now, scientists want to know whether or not there is a “Triangle Love” among N people. “Triangle Love” means that among any three people (A,B and C) , A loves B, B loves C and C loves A.
Your problem is writing a program to read the relationship among N people firstly, and return whether or not there is a “Triangle Love”.
[align=left]Input[/align]
The first line contains a single integer t (1 <= t <= 15), the number of test cases.
For each case, the first line contains one integer N (0 < N <= 2000).
In the next N lines contain the adjacency matrix A of the relationship (without spaces). Ai,j = 1 means i-th people loves j-th people, otherwise Ai,j = 0.
It is guaranteed that the given relationship is a tournament, that is, Ai,i= 0, Ai,j ≠ Aj,i(1<=i, j<=n,i≠j).
[align=left]Output[/align]
For each case, output the case number as shown and then print “Yes”, if there is a “Triangle Love” among these N people, otherwise print “No”.
Take the sample output for more details.
[align=left]Sample Input[/align]
2 5 00100 10000 01001 11101 11000 5 01111 00000 01000 01100 01110
[align=left]Sample Output[/align]
Case #1: Yes Case #2: No
题意:给你一个特殊的有向图,该有向图的随意两个节点u与v之间有且仅有一条单向边,如今问你该有向图是否存在由3个节点构成的环.
该图本质是拓扑排序题.假设该图能够拓扑排序,那么不存在3节点的环,否则存在3节点的环.
#include<cstdio> #include<iostream> #include<cstring> #include<queue> #include<algorithm> #include<vector> using namespace std; const int M = 2000 + 5; int n; int in[M]; char str[M]; int t; vector<int> map[M]; bool toposort() { int sum = 0; queue<int>Q; for(int i=0; i<n; i++) if( !in[i] ) Q.push( i ); while( !Q.empty() ) { int u = Q.front(); Q.pop(); sum++; for(int i=0; i<map[u].size(); i++) { int m = map[u][i]; if( --in[m] == 0 ) Q.push( m ); } } if( sum==n ) return true; else return false; } int main() { scanf( "%d", &t ); int cas; for( cas=1; cas<=t; cas++ ) { scanf( "%d", &n ); memset( in, 0, sizeof( in ) ); for( int i=0; i<n; i++ ) { map[i].clear(); scanf( "%s", str ); for( int j=0; j<n; j++ ) //for(int j=0; j<strlen(str); j++) //这么写会超时。复杂度会添加 { if( str[j]=='1' ) { map[i].push_back( j ); in[ j ]++; } } } printf("Case #%d: %s\n", cas, toposort()?"No":"Yes"); } return 0; }
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