POJ训练计划2983_Is the Information Reliable?(差分约束)

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