POJ 1306

#include<iostream>#include<string.h>//#include<mylib.h>#define size 10010using namespace std;class Union{ private: int *father; int *rank; int _size; public: Union(int _size){ this->_size=size; father=new int[_size]; rank=new int[_size]; } int findset(int v){ if(father[v]!=v){ father[v]=this->findset(father[v]); } return father[v]; } int unionset(int x,int y) { int fx=findset(x); int fy=findset(y); if(fx==fy)return fx; if(rank[fx]>rank[fy]){ rank[fx]+=rank[fy]; return father[fy]=fx; }else{ rank[fy]+=rank[fx]; return father[fx]=fy; } } void init(){ for(int i=0;i<_size;i++){ rank[i]=1; father[i]=i; } } ~Union(){ delete(father); delete(rank); }};int count;int tab[size];int dgr[size];int dgc[size];bool select[size];Union u(size);int f,c;void make(){ memset(dgr,0,sizeof(dgr)); memset(dgc,0,sizeof(dgc)); memset(tab,-1,sizeof(tab));}int main(){ // freopen("1.txt","r",stdin); int n=0; while(1){ n++; count=0; int e=0; u.init(); make(); while(1){ cin>>f>>c; if(f==-1&&c==-1)return 0; if(f==0&&c==0)break; e++; u.unionset(f,c); tab[f]=1; tab[c]=1; dgr[c]++; dgc[f]++; } for(int i=0;i<size;i++){ if(tab[i]==1){ f=u.findset(i); break; } } int flag=1; int dr=0; for(int i=0;i<size;i++){ if(tab[i]==1){ if(dgr[i]==0)dr++; int ans=u.findset(i); if(ans!=f||ans==-1||(dgr[i]>1)||(dr>1)){ flag=0; break; } } } if(flag&&dr==1||e==0)cout<<"Case "<<n<<" is a tree."<<endl; else cout<<"Case "<<n<<" is not a tree."<<endl; } return 0;}