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| Time Limit: 3000MS | Memory Limit: 131072K | |
| Total Submissions: 11560 | Accepted: 3658 |
Description
The galaxy war between the Empire Draco and the Commonwealth of Zibu broke out 3 years ago. Draco established a line of defense called Grot. Grot is a straight line with N defense stations. Because of the cooperation of the stations, Zibu’s Marine Glory cannot march any further but stay outside the line.
A mystery Information Group X benefits form selling information to both sides of the war. Today you the administrator of Zibu’s Intelligence Department got a piece of information about Grot’s defense stations’ arrangement from Information Group X. Your task is to determine whether the information is reliable.
The information consists of M tips. Each tip is either precise or vague.
Precise tip is in the form of P A B X, means defense station A is X light-years north of defense station B.
Vague tip is in the form of V A B, means defense station A is in the north of defense station B, at least 1 light-year, but the precise distance is unknown.
Input
There are several test cases in the input. Each test case starts with two integers N (0 < N ≤ 1000) and M (1 ≤ M ≤ 100000).The next M line each describe a tip, either in precise form or vague form.
Output
Output one line for each test case in the input. Output “Reliable” if It is possible to arrange N defense stations satisfying all the M tips, otherwise output “Unreliable”.
Sample Input
3 4 P 1 2 1 P 2 3 1 V 1 3 P 1 3 1 5 5 V 1 2 V 2 3 V 3 4 V 4 5 V 3 5
Sample Output
Unreliable Reliable
题意：如题
思路;用spfa须增设超级源点，所以又多了N条边，故TLE，而bellman_ford则可以直接处理
#include<iostream> #include<cstdio> #include<cstdlib> #include<cstring> #include<algorithm> using namespace std; const int maxn=10010; const int INF=(1<<28); int N,M; int a,b,x; struct Edge { int u,v,w; };Edge edge[maxn*100];int e; char ch; int dist[maxn]; void add_edge(int u,int v,int w) { edge[e++]={u,v,w}; } bool relax(int cur) { int tmp=dist[edge[cur].u]+edge[cur].w; if(tmp>dist[edge[cur].v]){ dist[edge[cur].v]=tmp; return true; } return false; } bool bellman_ford() { memset(dist,0,sizeof(dist)); for(int i=0;i<N;i++){ bool flag=0; for(int j=0;j<e;j++){ if(relax(j)) flag=1; } if(!flag) return true; } for(int i=0;i<e;i++){ if(relax(i)) return false; } return true; } int main() { while(cin>>N>>M){ e=0; char ch; while(M--){ getchar(); scanf("%c",&ch); if(ch==‘P‘){ //cin>>a>>b>>x; scanf("%d%d%d",&a,&b,&x); add_edge(b,a,x); add_edge(a,b,-x); } else{ scanf("%d%d",&a,&b); add_edge(b,a,1); } } if(bellman_ford()) cout<<"Reliable"<<endl; else cout<<"Unreliable"<<endl; } return 0; }
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原文地址：http://www.cnblogs.com/--560/p/4413013.html
