Submission #1065932

#	Time	Username	Problem	Language	Result	Execution time	Memory
1065932		Hugo1729	Race (IOI11_race)	C++17	100 / 100	729 ms	60348 KiB

race

#include <bits/stdc++.h>
#include "race.h"
using namespace std;
typedef long long ll;
 
vector<pair<ll,ll>> adj[200001];
ll sz[200001];
bool marked[200001]={0};
 
ll k;
 
ll dfs_sizes(ll v, ll pV){
    sz[v]=1;
    for(auto [w,d] : adj[v]){
        if(w!=pV&&!marked[w]){
            sz[v]+=dfs_sizes(w,v);
        }
    }
    return sz[v];
}
 
ll dfs_centroid(ll v, ll pV, ll subtree_sz){
    for(auto [w,d] : adj[v]){
        if(pV!=w&&!marked[w]&&sz[w]>=(subtree_sz/2)){
            return dfs_centroid(w,v,subtree_sz);
        }
    }
    return v;
}
 
void dfs_paths(ll v, ll pV,ll dist,ll l, vector<pair<ll,ll>> &a){
    if(dist<=k)a.push_back({dist,l});
    for(auto [w,d] : adj[v]){
        if(w!=pV&&!marked[w]){
            if(dist+d<=k){
                dfs_paths(w,v,dist+d,l+1,a);
            }
        }
    }
}
 
 
ll centroid_decomposition(ll v){
    ll c = dfs_centroid(v,v,dfs_sizes(v,v));
 
 
    marked[c]=1;
    
    ll ans=1000001;
    map<ll,ll> m;
    m[0]=0;
 
    for(auto [w,d] : adj[c]){
        if(!marked[w]){
            vector<pair<ll,ll>> a;
            dfs_paths(w,c,d,1,a);
 
            for(auto [dist,l] : a){
                if(m.count(k-dist)){
                    ans=min(ans,l+m[k-dist]);
                }
            }
            for(auto [dist,l] : a){
                if(m.count(dist))m[dist]=min(m[dist],l);
                else m[dist]=l;
            }
 
 
 
            ans = min(ans,centroid_decomposition(w));
        }
    }
 
    return ans;
}
 
 
 
 
int best_path(int N, int K, int H[][2], int L[]){
    for(ll i=0;i<N-1;i++){
        adj[H[i][0]].push_back({H[i][1],L[i]});
        adj[H[i][1]].push_back({H[i][0],L[i]});
    }
 
    k=K;
    ll ans = centroid_decomposition(0);
 
    return (ans==1000001?-1:ans);
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 57 / 57