POJ 3259 Wormholes(spfa判负环)
2015-08-19 11:01
405 查看
Wormholes
DescriptionWhile exploring his many farms, Farmer John has discovered a number of amazing wormholes. A wormhole is very peculiar because it is a one-way path that delivers you to its destination at a time that is BEFORE you entered the wormhole! Each of FJ's farms comprises N (1 ≤ N ≤ 500) fields conveniently numbered 1..N, M (1 ≤ M ≤ 2500) paths, and W (1 ≤ W ≤ 200) wormholes.
As FJ is an avid time-traveling fan, he wants to do the following: start at some field, travel through some paths and wormholes, and return to the starting field a time before his initial departure. Perhaps he will be able to meet himself :) .
To help FJ find out whether this is possible or not, he will supply you with complete maps to F (1 ≤ F ≤ 5) of his farms. No paths will take longer than 10,000 seconds to travel and no wormhole can bring FJ back in time by more than 10,000 seconds.
Input
Line 1: A single integer, F. F farm descriptions follow.
Line 1 of each farm: Three space-separated integers respectively: N, M, and W
Lines 2..M+1 of each farm: Three space-separated numbers (S, E, T) that describe, respectively: a bidirectional path between S and E that requires T seconds to traverse. Two fields might be connected by more than one path.
Lines M+2..M+W+1 of each farm: Three space-separated numbers (S, E, T) that describe, respectively: A one way path from S to E that also moves the traveler back T seconds.
Output
Lines 1..F: For each farm, output "YES" if FJ can achieve his goal, otherwise output "NO" (do not include the quotes).
Sample Input
2 3 3 1 1 2 2 1 3 4 2 3 1 3 1 3 3 2 1 1 2 3 2 3 4 3 1 8
Sample Output
NO YES
Hint
For farm 1, FJ cannot travel back in time.
For farm 2, FJ could travel back in time by the cycle
1->2->3->1, arriving back at his starting location 1 second
before he leaves. He could start from anywhere on the cycle to
accomplish this.
#include<cstdio> #include<queue> #include<cstring> #include<algorithm> using namespace std; const int maxn=550; const int maxm=2555; const int inf=0x3f3f3f3f; int G[maxn][maxn]; bool vis[maxn]; int used[maxn]; int d[maxn]; int cnt; int m,n1,n2; bool spfa(int s) { queue<int>q; memset(vis,0,sizeof(vis)); memset(d,inf,sizeof(d)); memset(used,0,sizeof(used)); d[s]=0; q.push(s); vis[s]=1; used[s]++; while(!q.empty()) { int u=q.front(); q.pop(); vis[u]=0; for(int i=1;i<=m;i++) { if(d[i]>d[u]+G[u][i]) { d[i]=d[u]+G[u][i]; if(!vis[i]) { if(used[i]>=maxn) return true; q.push(i); vis[i]=1; used[i]++; } } } } return false; } int main() { int t,u,v,w; scanf("%d",&t); while(t--) { memset(G,inf,sizeof(G)); scanf("%d%d%d",&m,&n1,&n2); for(int i=0;i<n1;i++) { scanf("%d%d%d",&u,&v,&w); G[u][v]=G[v][u]=min(G[u][v],w); } for(int i=0;i<n2;i++) { scanf("%d%d%d",&u,&v,&w); G[u][v]=min(G[u][v],-w); } int ans=spfa(1); if(ans) printf("YES\n"); else printf("NO\n"); } return 0; }
相关文章推荐
- iframe - 基本用法
- C#调用Web Service时的身份验证
- 网站运维如何监控云主机服务
- MFC中CTreeCtrl加载节点缓慢的分析和解决方法
- 虚拟机设置
- LintCode-交叉字符串
- js实现滑动条效果
- XML解析之jdom
- 在自定义cell里面实现跳转的方法
- 人脸性别识别文献阅读笔记(2)
- 利用ng-click、ng-switch和click-class制作切换的tabl
- 【LeetCode】168. Excel Sheet Column Title
- 深入理解Javascript window对象
- Python中的集合类型知识讲解
- 指针及地址笔记
- Hadoop自动化集群部署脚本
- bfs入门题 poj 1915 knight moves
- 利用HttpURLConnection下载文件的核心代码代码
- WCF Binding实例
- 隐藏系统布局的ProgressDialog中的button