(差分约束系统) poj 2983
| Time Limit: 3000MS | Memory Limit: 131072K | |
| Total Submissions: 11676 | Accepted: 3687 |
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
#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<cstdlib>
#include<algorithm>
#include<queue>
#define INF 100000000
using namespace std;
int n,m,cnt,in[1010],dist[1010];
bool vis[1010];
char c;
struct node
{
int to,len,next;
}e[210000];
int head[1010];
void add(int u,int v,int len)
{
e[++cnt].to=v;
e[cnt].len=len;
e[cnt].next=head[u];
head[u]=cnt;
}
bool spfa(int u)
{
memset(in,0,sizeof(in));
memset(vis,0,sizeof(vis));
for(int i=0;i<=n;i++)
dist[i]=INF;
vis[u]=1;
dist[u]=0;
queue<int> q;
q.push(u);
in[u]++;
while(!q.empty())
{
int x=q.front();
q.pop();
vis[x]=0;
for(int i=head[x];i;i=e[i].next)
{
int v=e[i].to;
int w=e[i].len;
if(dist[v]>dist[x]+w)
{
dist[v]=dist[x]+w;
if(!vis[v])
{
q.push(v);
vis[v]=1;
in[v]++;
if(in[v]>n+1)
return false;
}
}
}
}
return true;
}
int main()
{
int a,b,w;
while(scanf("%d%d",&n,&m)!=EOF)
{
cnt=1;
memset(head,0,sizeof(head));
for(int i=1;i<=m;i++)
{
cin>>c;
if(c=='P')
{
scanf("%d%d%d",&a,&b,&w);
add(b,a,-w);
add(a,b,w);
}
else if(c=='V')
{
scanf("%d%d",&a,&b);
add(b,a,-1);
}
}
for(int i=1;i<=n;i++)
add(0,i,0);
if(spfa(0))
printf("Reliable\n");
else
printf("Unreliable\n");
}
return 0;
}
