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;
    }
}