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poj2983--Is the Information Reliable?（差分约束）
| Time Limit: 3000MS | Memory Limit: 131072K | |
| Total Submissions: 11125 | Accepted: 3492 |
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 withN 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 stationB, 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 integersN (0 < N ≤ 1000) and M (1 ≤ M ≤ 100000).The nextM 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 arrangeN defense stations satisfying all the M tips, otherwise output “Unreliable”.
Sample Input
3 4P 1 2 1P 2 3 1V 1 3P 1 3 15 5V 1 2V 2 3V 3 4V 4 5V 3 5
Sample Output
UnreliableReliabl
给出了 P a b w 表示 b在a以北w公里， V a b 表示 b在a北边，最少1公里，问所有 的条件可不能够所有满足。
由P 能够得到 b - a = w 也就是b - a <= w && a - b <= w ，由 V a b 得到 b - a >= 1 也就是 a - b <= -1 ;建图，使用最短路，推断是否会有负环。初始dis要所有为0.
#include <cstdio>#include <cstring>#include <algorithm>struct node{ int u , v , w ;} p[300000];int dis[2000] , cnt ;void add(int u,int v,int w){ p[cnt].u = u ; p[cnt].v = v ; p[cnt++].w = w ;}int main(){ int i , j , n , m , u , v , w ; char str[10] ; while(scanf("%d %d", &n, &m)!=EOF) { cnt = 0 ; while(m--) { scanf("%s", str); if(str[0] == 'P') { scanf("%d %d %d", &u, &v, &w); add(u,v,-w); add(v,u,w); } else { scanf("%d %d", &u, &v); add(u,v,-1); } } memset(dis,0,sizeof(dis)); for(i = 1 ; i <= n ; i++) for(j = 0 ; j < cnt ; j++) if( dis[ p[j].v ] >dis[ p[j].u ] + p[j].w ) dis[ p[j].v ] = dis[ p[j].u ] + p[j].w ; for(j = 0 ; j < cnt ; j++) if( dis[ p[j].v ] > dis[ p[j].u ] + p[j].w ) break; if(j < cnt) printf("Unreliable\n"); else printf("Reliable\n"); }}
poj2983--Is the Information Reliable?（差分约束）