#include "race.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 2e5+7;
const int MAXL = 1e6+7;
const int INF = 1e8+7;
struct Node{
int to, w;
};
vector<vector<Node>> graph(MAXN,vector<Node>());
vector<bool> is_off(MAXN,false);
vector<int> sub_size(MAXN);
vector<pair<int, int>> minNodes(MAXL,{0, -1});
int res=MAXN;
void GetSubSizes(int v, int p){
sub_size[v]=1;
for(auto [u,w] : graph[v]){
if(is_off[u] || u==p) continue;
GetSubSizes(u,v);
sub_size[v] += sub_size[u];
}
}
int FindCentroid(int v, int p, int tree_size){
for(auto [u,_] : graph[v]){
if(is_off[u] || u==p) continue;
if(sub_size[u] > ((tree_size+1)/2)) return FindCentroid(u,v,tree_size);
}
return v;
}
void ResultDFS(int v, int p, int depth, int val, int k, int c){
if(val > k) return;
if (minNodes[k-val].second == c) res = res = min(res, minNodes[k-val].first+depth);
for(auto [u,w] : graph[v]){
if(is_off[u] || u==p) continue;
ResultDFS(u,v,depth+1,val+w,k,c);
}
}
void UpdateDFS(int v, int p, int depth, int val, int k, int c){
if(val > k) return;
if (minNodes[val].second == c) minNodes[val] = min(minNodes[val], {depth, c});
else minNodes[val] = {depth, c};
for(auto [u,w] : graph[v]){
if(is_off[u] || u==p) continue;
UpdateDFS(u,v,depth+1,val+w,k,c);
}
}
void ProcessCentroid(int centroid, int k){
minNodes[0]={0, centroid};
for(auto [u,w] : graph[centroid]){
if(is_off[u]) continue;
ResultDFS(u,centroid,1,w,k,centroid);
UpdateDFS(u,centroid,1,w,k,centroid);
}
}
void CentroidDecomposition(int v, int k){
GetSubSizes(v,v);
int centroid = FindCentroid(v,v,sub_size[v]);
ProcessCentroid(centroid,k);
is_off[centroid]=true;
for(auto [u,_] : graph[centroid]){
if(is_off[u]) continue;
CentroidDecomposition(u,k);
}
}
int best_path(int N, int K, int H[][2], int L[]) {
int n=N, k = K;
for(int i=0; i<n-1; ++i) {
int nodeA = H[i][0], nodeB = H[i][1], weight = L[i];
graph[nodeA].push_back({nodeB,weight});
graph[nodeB].push_back({nodeA,weight});
}
CentroidDecomposition(0,k);
if(res==MAXN) res=-1;
return res;
}
