(差分约束系统) poj 2983

Is the Information Reliable?

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

POJ Monthly--2006.08.27, Dagger

 

#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;
}