$P1547 Out of Hay$

(problem)
(kruskal)模板题(qwq)
((2 <= N <= 2,000))
所以边数是 (2000^2 /2) 不是 (2^{18})

#include <bits/stdc++.h>
using namespace std;
typedef long long LL ;
LL n,m,p;
LL s=-0x7f7f7f7f;
LL cnt=0;
LL f[1<<18] ;
struct node{
	int a,b,x;
}a[1<<18];
bool cmp (node x, node y) {
	return x.x<y.x;
}
inline int get(int x) {
	if (f[x]!=x) f[x]=get(f[x]);
	return f[x];
}
inline void kruskal() {
	register int cnt=0;
	register int x,y;
	for(register int i=1;i<=n;i++) f[i]=i;
	for(register int i=1;i<=m;i++) {
		x = get(a[i].a) ; y = get(a[i].b) ;
		if(x == y) continue;
		s= max(x,a[i].x);
		f[x]=y; cnt++;
		if (cnt == n-1) break;
	}
	if (cnt<n-1) cout << -1 << endl ;
	else cout << s << endl ;
} 
signed main() {
	ios::sync_with_stdio(false);
	cin >> n >> m ;
	for(register int i=1;i<=m;i++) cin >> a[i].a >> a[i].b >> a[i].x;
	sort(a+1,a+m+1,cmp) ;
	kruskal();
	return 0;
}