# | 제출 시각 | 아이디 | 문제 | 언어 | 결과 | 실행 시간 | 메모리 |
---|---|---|---|---|---|---|---|
1269279 | leanderson | 경주 (Race) (IOI11_race) | C++20 | 0 ms | 0 KiB |
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll MAXN = 1e5+50;
#define INF 0x3f3f3f3f
#define INFLL 0x3f3f3f3f3f3f3f3f
#define optimize ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define endl "\n"
#define yes() cout << "YES\n"
#define no() cout << "NO\n"
//------------------solution starts below------------------//
vector<set<pair<int,int>>> g_adj(MAXN);
vector <int> sub(MAXN);
vector <bool> removed(MAXN);
int n,k;
int answer = INF;
int dfs_size(int u, int p){
sub[u] = 1;
for (auto &pr : g_adj[u]){
int v = pr.first;
if (v == p || removed[v]) continue;
sub[u] += dfs_size(v, u);
}
return sub[u];
}
int dfs_find_centroid(int u, int p, int n){
for (auto &pr : g_adj[u]){
int v = pr.first;
if (v == p || removed[v]) continue;
if (sub[v] > n/2) return dfs_find_centroid(v, u, n);
}
return u;
}
void collect_paths(int u, int p, ll sum, int len, vector<pair<ll,int>> &out){
if (sum > k) return;
out.emplace_back(sum, len); // armazena (soma, comprimento)
for (auto &pr : g_adj[u]){
int v = pr.first;
int w = pr.second;
if (v == p || removed[v]) continue;
collect_paths(v, u, sum + w, len + 1, out);
}
}
void process_centroid(int centroid){
unordered_map<ll,int> best;
best.reserve(32);
best[0] = 0;
for (auto &pr : g_adj[centroid]){
int v = pr.first;
int w = pr.second;
if (removed[v]) continue;
vector<pair<ll,int>> paths;
collect_paths(v, centroid, w, 1, paths);
for (auto &pa : paths){
ll s = pa.first;
int len = pa.second;
if (best.find(k - s) != best.end()){
answer = min(answer, len + best[k - s]);
}
}
for (auto &pa : paths){
ll s = pa.first;
int len = pa.second;
auto it = best.find(s);
if (it == best.end() || len < it->second) best[s] = len;
}
}
}
void decompose(int start){
int n = dfs_size(start, -1);
int centroid = dfs_find_centroid(start, -1, n);
process_centroid(centroid);
removed[centroid] = true;
for (auto &pr : g_adj[centroid]){
int v = pr.first;
if (!removed[v]) decompose(v);
}
}
void organize_edges(vector<pair<int,int>> &edges, vector<int> &weights){
for (int i=0;i<n-1;i++){
int u = edges[i].first;
int v = edges[i].second;
int w = weights[i];
g_adj[u].insert({v,w});
g_adj[v].insert({u,w});
}
decompose(0);
if (answer == INF) cout << -1 << endl;
else cout << answer << endl;
}
void solve(){
cin >> n >> k;
vector<pair<int,int>> edges(n);
vector<int> weights(n);
for (int i=0;i<n-1;i++){
int u,v;
cin >> u >> v;
edges[i] = {u,v};
}
for (int i=0;i<n-1;i++){
int w;
cin >> w;
weights[i] = w;
}
organize_edges(edges,weights);
}
int main (){
optimize;
ll t;
t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}