#include <bits/stdc++.h>
using namespace std;
vector<vector<pair<int,int>>> grafo;
vector<int> subtrees;
vector<bool> visited;
int minCam;
vector<int> melhor, last_update;
int current_time = 0;
void calc_subtrees(int src, int parent){
subtrees[src] = 1;
for (auto& vz: grafo[src]){
int v = vz.first;
if (v == parent || visited[v]) continue;
calc_subtrees(v, src);
subtrees[src] += subtrees[v];
}
}
int centroid(int src, int parent, int subTreeSize){
for (auto vz: grafo[src]){
int v = vz.first;
if (v == parent || visited[v]) continue;
if (subtrees[v] > subTreeSize/2){
return centroid(v, src, subTreeSize);
}
}
return src;
}
int find_centroid(int beg, int parent){
calc_subtrees(beg, parent);
return centroid(beg, -1, subtrees[beg]);
}
inline int get_val(int x){
return (last_update[x] == current_time ? melhor[x] : INT_MAX);
}
inline void set_val(int x, int val){
if (last_update[x] != current_time){
last_update[x] = current_time;
melhor[x] = val;
} else {
melhor[x] = min(melhor[x], val);
}
}
void dfs1(int src, int parent, int currPathTam, int currPathArestas, int K){
if (visited[src] || currPathTam > K) return;
int need = K - currPathTam;
if (get_val(need) != INT_MAX)
minCam = min(minCam, currPathArestas + get_val(need));
for (auto &[vz, w] : grafo[src]){
if (vz == parent || visited[vz]) continue;
dfs1(vz, src, currPathTam + w, currPathArestas + 1, K);
}
}
void dfs2(int src, int parent, int currPathTam, int currPathArestas, int K){
if (visited[src] || currPathTam > K) return;
set_val(currPathTam, currPathArestas);
for (auto &[vz, w]: grafo[src]){
if (vz == parent || visited[vz]) continue;
dfs2(vz, src, currPathTam + w, currPathArestas + 1, K);
}
}
void solve(int start, int K){
int cntd = find_centroid(start, -1);
visited[cntd] = true;
current_time++;
set_val(0, 0);
for (auto &[v, w] : grafo[cntd]){
if (visited[v]) continue;
dfs1(v, cntd, w, 1, K);
dfs2(v, cntd, w, 1, K);
}
for (auto &[v, w] : grafo[cntd]){
if (!visited[v]){
solve(v, K);
}
}
}
int best_path(int N, int K, int H[][2], int L[]){
minCam = INT_MAX;
visited.assign(N, false);
subtrees.assign(N, 0);
grafo.assign(N, {});
melhor.assign(K+1, INT_MAX);
last_update.assign(K+1, -1);
current_time = 0;
for (int i = 0; i < N - 1; i++){
grafo[H[i][0]].push_back({H[i][1], L[i]});
grafo[H[i][1]].push_back({H[i][0], L[i]});
}
solve(0, K);
return (minCam == INT_MAX ? -1 : minCam);
}
