并查集

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#define N 1000010
using namespace std;
int fa[N];
int find(int x)
{
    if(fa[x]==x) return x;
    int t=find(fa[x]);
    fa[x]=t;
    return t;
    //return fa[x]==x?x:fa[x]=find(fa[x]);
}
void merge(int x,int y)
{
    x=find(x);
    y=find(y);
    if(x==y) return;
    fa[x]=y;
}
int m,x[N],y[N],f[N];
void doit()
{
    memset(fa,0,sizeof(fa));
    for(int i=1;i<=1000000;i++) fa[i]=i;
    cin>>m;
    for(int i=1;i<=m;i++)
    {
        cin>>x[i]>>y[i]>>f[i];
        if(f[i]==1) merge(x[i],y[i]);
    }
    bool ans=true;
    for(int i=1;i<=m;i++)
    {
        if(f[i]==0)
        {
            if(find(x[i])==find(y[i])) ans=false;
        }
    }
    puts(ans?"YES":"NO");
}
int main()
{
    int T;
    cin>>T;
    while(T--) doit();
}