| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 1244022 | nguyenhuythach | 경주 (Race) (IOI11_race) | C++20 | 0 ms | 0 KiB |
//luoi code qua chep tam code cu:)
#include<bits/stdc++.h>
#define ii pair<int,int>
#define fi first
#define se second
using namespace std;
const int N = 1e6;
const int K = 1e6;
const int INF = 1e9;
int n, k, sz[N+10], bigc[N+10], st[N+10], fst[N+10], en[N+10], f[N+10], h[N+10], timer, res = INF;
vector<ii> adj[N+10];
map<int,int> mn;
void dfs(int u, int pu){
sz[u]=1;
st[u] = ++timer;
fst[timer] = u;
for (ii p: adj[u]){
int v = p.fi;
int w = p.se;
if (v==pu) continue;
f[v] = f[u]+w;
h[v] = h[u]+1;
if (f[v]==k) res = min(res, h[v]);
dfs(v,u);
sz[u]+=sz[v];
if (sz[v]>sz[bigc[u]]) bigc[u]=v;
}
en[u] = timer;
}
void sackadd(int u){
if (!mn[f[u]]) mn[f[u]]=INF;
mn[f[u]] = min(mn[f[u]], h[u]);
}
void sacksub(int u){
mn[f[u]] = INF;
}
void Sack(int u, int pu){
for (ii p: adj[u]){
int v = p.fi;
if (v==pu || v==bigc[u]) continue;
Sack(v,u);
for (int i=st[v];i<=en[v];i++) sacksub(fst[i]);
}
if (bigc[u]) Sack(bigc[u], u);
if (mn[f[u]+k]==0) mn[f[u]+k] = INF;
res = min(res, mn[f[u]+k]-h[u]);
sackadd(u);
for (ii p: adj[u]){
int v = p.fi;
if (v==pu || v==bigc[u]) continue;
for (int i=st[v];i<=en[v];i++){
int c = k-(f[fst[i]]-f[u])+f[u];
if (mn[c]==0) mn[c] =INF;
if (c>=0) res = min(res, mn[c]+h[fst[i]]-2*h[u]);
}
for (int i=st[v];i<=en[v];i++) sackadd(fst[i]);
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin>>n>>k;
for (int i=1;i<n;i++){
int u,v,w; cin>> u>>v>>w;
u++; v++;
adj[u].push_back({v,w});
adj[v].push_back({u,w});
}
dfs(1,0);
Sack(1,0);
cout <<(res>=2e5?-1:res);
}