mirror of
https://git.sb/baoshuo/OI-codes.git
synced 2024-12-25 18:32:00 +00:00
117 lines
2.2 KiB
C++
117 lines
2.2 KiB
C++
|
#include <iostream>
|
||
|
#include <limits>
|
||
|
#include <set>
|
||
|
#include <vector>
|
||
|
|
||
|
using std::cin;
|
||
|
using std::cout;
|
||
|
const char endl = '\n';
|
||
|
|
||
|
const int N = 2e5 + 5;
|
||
|
|
||
|
int n, k, ans = std::numeric_limits<int>::max();
|
||
|
int root, siz[N], max[N];
|
||
|
int cnt;
|
||
|
std::pair<int, int> dist[N];
|
||
|
bool vis[N];
|
||
|
std::vector<std::pair<int, int>> g[N];
|
||
|
|
||
|
void find(int u, int fa, int tot) {
|
||
|
siz[u] = 1;
|
||
|
max[u] = 0;
|
||
|
|
||
|
for (auto e : g[u]) {
|
||
|
int v = e.first,
|
||
|
w = e.second;
|
||
|
|
||
|
if (v == fa || vis[v]) continue;
|
||
|
|
||
|
find(v, u, tot);
|
||
|
|
||
|
siz[u] += siz[v];
|
||
|
max[u] = std::max(max[u], siz[v]);
|
||
|
}
|
||
|
|
||
|
max[u] = std::max(max[u], tot - siz[u]);
|
||
|
|
||
|
if (max[u] < max[root]) root = u;
|
||
|
}
|
||
|
|
||
|
void dis(int u, int fa, int w, int l) {
|
||
|
if (w > k || l > ans) return;
|
||
|
|
||
|
dist[++cnt] = std::make_pair(w, l);
|
||
|
|
||
|
for (auto e : g[u]) {
|
||
|
int _v = e.first,
|
||
|
_w = e.second;
|
||
|
|
||
|
if (_v == fa || vis[_v]) continue;
|
||
|
|
||
|
dis(_v, u, w + _w, l + 1);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
void calc(int u) {
|
||
|
std::set<std::pair<int, int>> set;
|
||
|
|
||
|
set.insert(std::make_pair(0, 0));
|
||
|
|
||
|
for (auto e : g[u]) {
|
||
|
int v = e.first,
|
||
|
w = e.second;
|
||
|
|
||
|
if (vis[v]) continue;
|
||
|
|
||
|
cnt = 0;
|
||
|
dis(v, u, w, 1);
|
||
|
|
||
|
for (int i = 1; i <= cnt; i++) {
|
||
|
auto it = set.lower_bound(std::make_pair(k - dist[i].first, 0));
|
||
|
|
||
|
if (it != set.end() && it->first + dist[i].first == k) {
|
||
|
ans = std::min(ans, it->second + dist[i].second);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
for (int i = 1; i <= cnt; i++) set.insert(dist[i]);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
void solve(int u) {
|
||
|
vis[u] = true;
|
||
|
calc(u);
|
||
|
|
||
|
for (auto e : g[u]) {
|
||
|
int v = e.first,
|
||
|
w = e.second;
|
||
|
|
||
|
if (vis[v]) continue;
|
||
|
|
||
|
max[root = 0] = std::numeric_limits<int>::max();
|
||
|
find(v, 0, siz[v]);
|
||
|
solve(root);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
int main() {
|
||
|
std::ios::sync_with_stdio(false);
|
||
|
|
||
|
cin >> n >> k;
|
||
|
|
||
|
for (int i = 1, u, v, w; i < n; i++) {
|
||
|
cin >> u >> v >> w;
|
||
|
|
||
|
g[u + 1].push_back(std::make_pair(v + 1, w));
|
||
|
g[v + 1].push_back(std::make_pair(u + 1, w));
|
||
|
}
|
||
|
|
||
|
max[root = 0] = n;
|
||
|
find(1, 0, n);
|
||
|
solve(root);
|
||
|
|
||
|
cout << (ans == std::numeric_limits<int>::max() ? -1 : ans) << endl;
|
||
|
|
||
|
return 0;
|
||
|
}
|