记录编号	596449	评测结果	AAAAAAAAAAAAAAAAAAAA
题目名称	[NOIP 2018]赛道修建	最终得分	100
用户昵称	┭┮﹏┭┮	是否通过	通过
代码语言	C++	运行时间	2.706 s
提交时间	2024-10-28 08:47:25	内存使用	8.49 MiB

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,ll>
#define fi first
#define in inline
#define se second
#define mp make_pair
#define pb push_back
const int N = 5e4+10;

ll read(){
	ll x = 0,f = 1;char c = getchar();
	for(;c < '0' || c > '9';c = getchar())if(c == '-')f = -1;
	for(;c >= '0' && c <= '9';c = getchar())x = (x<<1) + (x<<3) + c-'0';
	return x * f;
}




int n,m;
vector<pii>e[N];

int sum;
multiset<ll>s[N];
ll dfs(int x,int fa,ll mid){
	for(auto it : e[x]){
		int y = it.fi;
		if(y == fa)continue;
		ll l = dfs(y,x,mid) + it.se;
		if(l >= mid)sum++;
		else s[x].insert(l);
	}
	ll mx = 0;
	while(!s[x].empty()){
		if(s[x].size() == 1){
			mx = max(mx,*s[x].begin()),s[x].erase(s[x].begin());
			break;
		}
		auto it = s[x].lower_bound(mid - *s[x].begin());
		if(it == s[x].begin() && s[x].count(*it) == 1)it++;
		if(it == s[x].end()){
			mx = max(mx,*s[x].begin());
			s[x].erase(s[x].begin());
		}
		else{
			sum++;
			s[x].erase(s[x].find(*s[x].begin())),s[x].erase(s[x].find(*it));
		}
	}
	return mx;
}

bool check(ll mid){
	sum = 0;
	dfs(1,0,mid);
	return sum >= m;
}

int main(){
	freopen("2018track.in","r",stdin);
	freopen("2018track.out","w",stdout);
	n = read(),m = read();
	for(int i = 1;i < n;i++){
		int x = read(),y = read();ll z = read();
		e[x].pb({y,z}),e[y].pb({x,z});
	}
	ll l = 0,r = 1e9;
	while(l < r){
		ll mid = l + r + 1 >> 1;
		if(check(mid))l = mid;
		else r = mid - 1;
	}
	printf("%lld\n",l);

	return 0;

}