#include "race.h" #include <bits/stdc++.h> using namespace std; #define name "TENBAI" #define fi first #define se second #define endl '\n' #define setmin(x, y) x = min((x), (y)) #define setmax(x, y) x = max((x), (y)) #define sqr(x) ((x) * (x)) #define all(x) x.begin(), x.end() const int inf = 1e9; const int NM = 2e5 + 5; vector<pair<int, int>> g[NM]; int n, k, ans = inf, done[NM], sz[NM]; map<int, int> mp; int dfs_sz(int u, int p) { sz[u] = 1; for (auto v : g[u]) if (v.fi != p && !done[v.fi]) sz[u] += dfs_sz(v.fi, u); return sz[u]; } int findcen(int u, int p, int SZ) { for (auto v : g[u]) if (v.fi != p && !done[v.fi] && 2 * sz[v.fi] >= SZ) return findcen(v.fi, u, SZ); return u; } void get(int u, int p, int w, int c) { if (mp.count(k - w)) setmin(ans, c + mp[k - w]); for (auto v : g[u]) if (v.fi != p && !done[v.fi]) get(v.fi, u, w + v.se, c + 1); } void add(int u, int p, int w, int c) { if (mp.count(w)) setmin(mp[w], c); else mp[w] = c; for (auto v : g[u]) if (v.fi != p && !done[v.fi]) get(v.fi, u, w + v.se, c + 1); } void cen(int u) { int c = findcen(u, 0, dfs_sz(u, 0)); mp.clear(); mp[0] = 0; for (auto v : g[c]) if (!done[v.fi]) { get(v.fi, c, v.se, 1); add(v.fi, c, v.se, 1); } done[c] = 1; for (auto v : g[c]) if (!done[v.fi]) cen(v.fi); } int best_path(int N, int K, int H[][2], int L[]) { n = N; k = K; for (int i = 0; i < n - 1; i++) { g[H[i][0]].emplace_back(H[i][1], L[i]); g[H[i][1]].emplace_back(H[i][0], L[i]); } cen(0); return ans == inf ? -1 : ans; }