poj 2983——Is the Information Reliable?

差分约束

#include<cstdio>#include<iostream>#include<cstring>#include<queue>using namespace std;#define INF 10000001int n,m,cnt;int head[350001],v[350001],w[350001],next[350001];int dis[1005],vis[1005],output[1005];void add(int a,int b,int c){v[cnt]=b;w[cnt]=c;next[cnt]=head[a];head[a]=cnt++;}bool spfa(){for(int i=1;i<=n;i++)dis[i]=-INF;memset(vis,0,sizeof(vis));memset(output,0,sizeof(output));queue<int> q;q.push(0);dis[0]=0;vis[0]=1;while(!q.empty()){int u=q.front();q.pop();vis[u]=0;output[u]++;if(output[u]>n)return 0;for(int i=head[u];i!=-1;i=next[i])if(dis[v[i]]<dis[u]+w[i]){dis[v[i]]=dis[u]+w[i];if(!vis[v[i]]){vis[v[i]]=1;q.push(v[i]);}}}return 1;}int main(){while(~scanf("%d%d",&n,&m)){getchar();memset(head,-1,sizeof(head));cnt=0;char a[10];int x,y,z;for(int i=0;i<m;i++){scanf("%s",a);if(a[0]=='P'){scanf("%d%d%d",&x,&y,&z);add(y,x,z);add(x,y,-z);}else{scanf("%d%d",&x,&y);add(y,x,1);}}for(int i=1;i<=n;i++)add(0,i,0);if(spfa())cout<<"Reliable"<<endl;elsecout<<"Unreliable"<<endl;}return 0;}