解题报告
思路:
求解:
p:a-b=x
v:a-b>=1
的方程
#include <iostream> #include <cstring> #include <cstdio> #include <queue> #define inf 0x3f3f3f3f using namespace std; struct node { int v,w,next; } edge[220000]; int head[1111],dis[1111],vis[1111],coun[1111],cnt,n,m,s,t,f; void add(int u,int v,int w) { edge[cnt].v=v; edge[cnt].w=w; edge[cnt].next=head[u]; head[u]=cnt++; } void spfa() { for(int i=0;i<=n;i++) { dis[i]=inf; vis[i]=0; } dis[s]=0; vis[s]=1; queue<int >Q; Q.push(s); while(!Q.empty()) { int u=Q.front(); Q.pop(); vis[u]=0; for(int i=head[u];i!=-1;i=edge[i].next) { int v=edge[i].v; if(dis[v]>dis[u]+edge[i].w) { dis[v]=dis[u]+edge[i].w; if(!vis[v]) { coun[v]++; if(coun[v]>n) { f=1; break; } vis[v]=1; Q.push(v); } } } } } int main() { int i,j,u,v,w; char ch[10]; while(~scanf("%d%d",&n,&m)) { s=f=0; memset(head,-1,sizeof(head)); memset(coun,0,sizeof(coun)); cnt=0; for(i=0; i<m; i++) { scanf("%s%d%d",ch,&u,&v); if(ch[0]=='P') { scanf("%d",&w); add(v,u,w); add(u,v,-w); } else { add(u,v,-1); } } for(i=1; i<=n; i++) { add(0,i,0); } spfa(); if(f) printf("Unreliable\n"); else printf("Reliable\n"); } return 0; }
Is the Information Reliable?
Time Limit: 3000MS | Memory Limit: 131072K | |
Total Submissions: 11068 | Accepted: 3463 |
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
Source
POJ Monthly--2006.08.27, Dagger