【题目链接】

           ​​https://www.lydsy.com/JudgeOnline/problem.php?id=4195​​

【算法】

            并查集

【代码】

           



#include<bits/stdc++.h>
using namespace std;
#define MAXN 1000010

struct info
{
        int u,v,w;
} a[MAXN];

int i,n,len,T;
int l[MAXN],r[MAXN],c[MAXN],fa[MAXN<<1],t[MAXN<<1];
bool flag;

inline int get_root(int x)
{
        if (fa[x] == x) return x;
        return fa[x] = get_root(fa[x]);
}
inline void merge(int u,int v)
{
        int sx = get_root(u),
                sy = get_root(v);
        fa[sx] = sy;
}
inline bool cmp(info a,info b)
{
        return a.w > b.w;        
}

int main() 
{
        
        scanf("%d",&T);
        while (T--)
        {
                scanf("%d",&n);
                len = 0;
                for (i = 1; i <= n; i++) 
                {
                        scanf("%d%d%d",&l[i],&r[i],&c[i]);
                        t[++len] = l[i];
                        t[++len] = r[i];
                }
                sort(t+1,t+len+1);
                len = unique(t+1,t+len+1) - t - 1;
                for (i = 1; i <= n; i++)
                {
                        a[i].u = lower_bound(t+1,t+len+1,l[i]) - t;
                        a[i].v = lower_bound(t+1,t+len+1,r[i]) - t;
                        a[i].w = c[i];
                }
                sort(a+1,a+n+1,cmp);
                for (i = 1; i <= len; i++) fa[i] = i;
                for (i = 1; i; i++)
                {
                        if (a[i].w == 1)
                                merge(a[i].u,a[i].v);
                        else break;
                }
                flag = false;
                for (; i <= n; i++)
                {
                        if (get_root(a[i].u) == get_root(a[i].v))
                        {
                                flag = true;
                                break;
                        }
                }
                if (flag) printf("NO\n");
                else printf("YES\n");
        }
         
        return 0;
    
}