poj 2883——Points

差分約束

注意點是要建立一個超級原點 防止有多個分圖出現

#include<queue>#include<iostream>#include<cstdio>using namespace std;#define INF 10000001#define esp 1int n,m;int head[2][30015],v[2][30015],next[2][30015];double w[2][30015];double dis[1005];int input[1505],output[1505];int cnt[2];void add(int k,int a,int b,double c){v[k][cnt[k]]=b;w[k][cnt[k]]=c;next[k][cnt[k]]=head[k][a];head[k][a]=cnt[k]++;}bool spfa(int k){for(int i=1;i<=n;i++)dis[i]=-INF;memset(input,0,sizeof(input));memset(output,0,sizeof(output));queue<int> q;q.push(0);dis[0]=0;input[0]=1;while(!q.empty()){int u=q.front();q.pop();input[u]=0;output[u]++;if(output[u]>n)return 0;for(int i=head[k][u];i!=-1;i=next[k][i])if(dis[v[k][i]]<dis[u]+w[k][i]){dis[v[k][i]]=dis[u]+w[k][i];if(!input[v[k][i]]){q.push(v[k][i]);input[v[k][i]]=1;}}}return 1;}int main(){int t;scanf("%d",&t);while(t--){memset(head,-1,sizeof(head));memset(cnt,0,sizeof(cnt));scanf("%d%d",&n,&m);for(int i=1;i<=n;i++){add(0,0,i,0);add(1,0,i,0);}for(int i=0;i<m;i++){int x,z;char y[10];scanf("%d%s%d",&x,&y,&z);if(y[0]=='N'&&y[1]=='E'){add(0,x,z,esp);//zyadd(1,x,z,esp);//sxcontinue;}if(y[0]=='N'&&y[1]=='W'){add(0,z,x,esp);add(1,x,z,esp);continue;}if(y[0]=='N'&&y[1]=='\0'){add(0,x,z,0);add(0,z,x,0);add(1,x,z,esp);continue;}if(y[0]=='S'&&y[1]=='E'){add(0,x,z,esp);add(1,z,x,esp);continue;}if(y[0]=='S'&&y[1]=='W'){add(0,z,x,esp);add(1,z,x,esp);continue;}if(y[0]=='S'&&y[1]=='\0'){add(0,x,z,0);add(0,z,x,0);add(1,z,x,esp);continue;}if(y[0]=='E'){add(0,x,z,esp);add(1,x,z,0);add(1,z,x,0);continue;}if(y[0]=='W'){add(0,z,x,esp);add(1,x,z,0);add(1,z,x,0);continue;}}if(spfa(0)&&spfa(1))cout<<"POSSIBLE"<<endl;elsecout<<"IMPOSSIBLE"<<endl;}return 0;}