PAT A 1118. Birds in Forest (25)【并查集】

并查集合并

#include<iostream>
using namespace std;
const int MAX = 10010;
int father[MAX],root[MAX];
int findfather(int x){if(x==father[x]) return x;else{int F=findfather(father[x]);father[x]=F;return F;}
}
void Union(int a , int b){int faA=findfather(a);int fbB=findfather(b);if(faA!=fbB){father[faA]=fbB;} 
}
void init(){for(int i=0;i<MAX;i++){father[i]=i;root[i]=0;}
} 
int n,q;
int main(){init();cin>>n;int maxbirds=0; for(int i=0;i<n;i++){int nbirds,firstbird;scanf("%d%d",&nbirds,&firstbird);if(firstbird>maxbirds) maxbirds=firstbird;for(int j=1;j<nbirds;j++){int bird;scanf("%d",&bird);if(bird>maxbirds) maxbirds=bird;Union(firstbird,bird);}}int trees=0;for(int i=1;i<=maxbirds;i++){int fa=findfather(i);root[fa]++;if(root[fa]==1) trees++;}printf("%d %d\n",trees,maxbirds);cin>>q;while(q--){int a , b;scanf("%d%d",&a,&b);if(findfather(a)==findfather(b)) printf("Yes\n");else printf("No\n");}
}

非递归压缩并查集

int father[MAX];  
bool isRoot[MAX];//判根  int findFather( int x ) {  int a = x;  while( x != father[x] ) {  x = father[x];  }  while( a != father[a] ) {  int z = a;  a = father[a];  father[z] = x;  }  return x;  
}  void Union( int a, int b ) {  int faA = findFather( a );  int faB = findFather( b );    if( faA != faB ) {  father[faA] = faB;  }  
}  void init( int n ) {  for( int i = 1; i <= n; i++ ) {  //从1开始father[i] = i;  isRoot[i] = false;  }  
}