poj 2983 Is the Information Reliable?

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等号的情况可以转换成不等式

a=b 就可以表示成a>=b b>=a

约束条件写出来就用bellman-ford

需要注意的是要构造超级源点

#include<stdio.h>#include<string.h>#include<stdlib.h>#include<math.h>#include<limits.h>struct edge{int u,v,w;}edges[500001];char ch[100];int dist[1001];int main(){    int n,mm,m;    int u,v;    while(scanf("%d%d",&n,&mm)==2){        m=0;        for(int i=1;i<=mm;i++){            scanf("%s",&ch);            if (ch[0]=='V'){                m++;                scanf("%d%d",&edges[m].v,&edges[m].u);                edges[m].w=-1;                }            if (ch[0]=='P'){                m++;                scanf("%d%d%d",&edges[m].v,&edges[m].u,&edges[m].w);                edges[m].w=-edges[m].w;                m++;                edges[m].u=edges[m-1].v;edges[m].v=edges[m-1].u;                edges[m].w=-edges[m-1].w;                }        }        bool flag=true;        int u,v;        for (int i=0;i<=n;i++) dist[i]=0;        dist[1]=0;        for (int i=1;i<=n;i++){            for (int j=1;j<=m;j++){                if (dist[edges[j].v]>dist[edges[j].u]+edges[j].w)                           dist[edges[j].v]=dist[edges[j].u]+edges[j].w;            }        }        for (int j=1;j<=m;j++){          if (dist[edges[j].v]>dist[edges[j].u]+edges[j].w) {                                         flag=false;                                         break;                                        }        }        if (!flag) printf("Unreliable\n");                            else printf("Reliable\n");    }    return 0;}