#include "race.h"
#include<bits/stdc++.h>
using namespace std;
vector< vector< pair<int, int> > > edges;
int size_of_subtree[200005], blocked[200005];
unordered_map <int, int> big, small;
int answer = INT_MAX;
void get_size_of_subtree(int current_node, int parent) {
size_of_subtree[current_node] = 1;
for (auto child : edges[current_node]) {
if (child.first != parent) {
get_size_of_subtree(child.first, current_node);
size_of_subtree[current_node] += size_of_subtree[child.first];
}
}
}
int get_centroid(int current_node) {
for (auto child : edges[current_node]) {
if (blocked[child.first] == 0 && size_of_subtree[child.first] > size_of_subtree[current_node] / 2) {
int total_size = size_of_subtree[current_node];
size_of_subtree[current_node] -= size_of_subtree[child.first];
size_of_subtree[child.first] = total_size;
return get_centroid(child.first);
}
}
return current_node;
}
void dfs(int current_node, int parent, int sum, int depth) {
if (small.find(sum) == small.end()) small[sum] = depth;
else small[sum] = min(small[sum], depth);
for (auto child : edges[current_node]) {
if (blocked[child.first] == 0 && child.first != parent) {
dfs(child.first, current_node, sum + child.second, depth + 1);
}
}
}
void solve(int current_node, int sum) {
big.clear();
current_node = get_centroid(current_node);
blocked[current_node] = 1;
big[0] = 0;
for (auto child : edges[current_node]) {
small.clear();
if (blocked[child.first] == 1) continue;
dfs(child.first, current_node, child.second, 1);
for (auto value : small) {
if (big.find(sum - value.first) != big.end()) answer = min(answer, big[sum - value.first] + small[value.first]);
}
for (auto value : small) {
if (big.find(value.first) == big.end()) big[value.first] = small[value.first];
else big[value.first] = min(big[value.first], small[value.first]);
}
}
for (auto child : edges[current_node]) {
if (blocked[child.first] == 0) solve(child.first, sum);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
edges.resize(N+1);
for (int i = 0; i < N - 1; i++) {
edges[H[i][0]].push_back(make_pair(H[i][1], L[i]));
edges[H[i][1]].push_back(make_pair(H[i][0], L[i]));
}
get_size_of_subtree(0, -1);
solve(0, K);
if (answer == INT_MAX) answer = -1;
return answer;
}
