1 P3367 【模板】并查集

参考资料

#include<bits/stdc++.h>
using namespace std;
const int M=2e5+10,N=1e4+10;
int n,m,x,y,z;
int pre[N];
int rk[N];
int find(int x){
	if(pre[x]==x) return x;
	return pre[x]=find(pre[x]);
}
bool isSame(int x,int y){
	return find(x)==find(y);
}
void join(int x,int y){
	x=find(x);
	y=find(y);
	if(x==y) return;
	if(rk[x]>rk[y]) pre[y]=x;
	else{
		if(rk[x]==rk[y]) rk[y]++;
		pre[x]=y;
	}
}
int main(){
	ios::sync_with_stdio(false);
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		pre[i]=i;
		rk[i]=1;
	}
	while(m--){
		cin>>z>>x>>y;
		if(z==1){
			join(x,y);
		}else if(z==2){
			if(isSame(x,y)) cout<<"Y"<<endl;
			else cout<<"N"<<endl;
		}
	}
	return 0;
} 

2 P1551 亲戚

还是并查集

#include<bits/stdc++.h>
using namespace std;
const int N=5e3+100;
int n,m,p;
int pre[N];
int rk[N];
int find(int x){
	if(pre[x]==x) return x;
	return pre[x]=find(pre[x]);
}
bool isSame(int x,int y){
	return find(x)==find(y);
}
void join(int x,int y){
	x=find(x);
	y=find(y);
	if(x==y) return;
	if(rk[x]>rk[y]) pre[y]=x;
	else{
		if(rk[x]==rk[y]) rk[y]++;
		pre[x]=y;
	}
}
int main(){
	ios::sync_with_stdio(0);
	cin>>n>>m>>p;
	for(int i=1;i<=n;i++){
		pre[i]=i;
		rk[i]=1;
	}
	while(m--){
		int x,y;
		cin>>x>>y;
		join(x,y);
	}
	while(p--){
		int a,b;
		cin>>a>>b;
		if(isSame(a,b)) cout<<"Yes"<<endl;
		else cout<<"No"<<endl;
	}
	return 0;
}

3 P2078 朋友

还是并查集

#include<bits/stdc++.h>
using namespace std;
const int N=2e4+100;
int n,m,p,q,x,y;
int pre[N];
int rk[N];
int find(int x){
	if(pre[x]==x) return x;
	return pre[x]=find(pre[x]);
}
bool isSame(int x,int y){
	return find(x)==find(y);
}
void join(int x,int y){
	x=find(x);
	y=find(y);
	if(rk[x]>rk[y]) pre[y]=x;
	else{
		if(rk[x]==rk[y]) rk[y]++;
		pre[x]=y;
	}
}
int main(){
	ios::sync_with_stdio(false);
	cin>>n>>m>>p>>q;
	for(int i=1;i<=n;i++){
		pre[i]=i;
		rk[i]=1;
	}
	for(int i=n+1;i<=n+m;i++){
		pre[i]=i;
		rk[i]=1;
	}
	rk[1]=N;rk[n+1]=N;
	while(p--){
		cin>>x>>y;
		join(x,y);
	}
	while(q--){
		cin>>x>>y;
		x*=-1;y*=-1;
		join(x+n,y+n);
	}
	int ans1=0,ans2=0;
	for(int i=1;i<=n;i++){
		if(find(i)==1) ans1++;
	}
	for(int i=n+1;i<=n+m;i++){
		if(find(i)==n+1) ans2++;
	}
	cout<<min(ans1,ans2)<<endl;
	return 0;
}