poj1611并查集

这道题用并查集效率很高。 #include<iostream> #include<string.h> #include<fstream> using namespace std; int n,m; int students[30000]; int find(int f) { int p=f; while(p!=0&&students[p]>=0) p=students[p]; while(p!=0&&students[f]>=0) { int temp=students[f]; students[f]=p; f=temp; } return p; } void uni(int f1,int f2) { int r1=find(f1); int r2=find(f2); if(r1==r2) return; if(students[r1]==0||students[r2]==0) { if(students[r1]==0) { students[r2]=r1; } else { students[r1]=r2; } } else { if(students[r1]<=students[r2]) { students[r1]+=students[r2]; students[r2]=r1; } else { students[r2]+=students[r1]; students[r1]=r2; } } } int main() { freopen("input.txt","r",stdin); while(scanf("%d %d",&n,&m)!=EOF) { if(m==0&&n==0) break; memset(students,-1,sizeof(int)*n); students[0]=0; for(int i=0;i<m;i++) { int k; scanf("%d",&k); int first; scanf("%d",&first); for(int j=1;j<k;j++) { int temp; scanf("%d",&temp); uni(first,temp); } } int count=0; for(int i=0;i<n;i++) { if(find(i)==0) count++; } printf("%d\n",count); } return 0; }