Submission #923073

#	Time	Username	Problem	Language	Result	Execution time	Memory
923073		Aiperiii	Valley (BOI19_valley)	C++14	100 / 100	326 ms	54148 KiB

valley

#include <bits/stdc++.h>
#define int long long
#define ff first
#define ss second
#define pb push_back
#define all(x) x.begin(),x.end()
using namespace std;
const int N=1e5+5;
vector <pair <int,int > > g[N];
int d[N],par[N],jmp[N][20],dis[N],shop[N],dis2[N],jmp_mn[N][20];
void dfs(int v,int p){
   par[v]=p;
   for(auto to : g[v]){
      if(to.ff!=p){
         dis[to.ff]=dis[v]+to.ss;
         d[to.ff]=d[v]+1;
         dfs(to.ff,v);
      }
   }
}
void dfs2(int v,int p){
   for(auto to : g[v]){
      if(to.ff!=p)dfs2(to.ff,v);
   }
   if(shop[v])dis2[v]=dis[v];
   dis2[p]=min(dis2[p],dis2[v]);
}
int lca(int a,int b){
   if(d[a]<d[b])swap(a,b);
   for(int i=19;i>=0;i--){
      if(d[jmp[a][i]]>=d[b]){
         a=jmp[a][i];
      }
   }
   if(a==b)return a;
   for(int i=19;i>=0;i--){
      if(jmp[a][i]!=jmp[b][i]){
         a=jmp[a][i];
         b=jmp[b][i];
      }
   }
   return par[a];
}
signed main(){
   ios_base::sync_with_stdio();
   cin.tie(0);cout.tie(0);
   int n,s,q,e;
   cin>>n>>s>>q>>e;
   vector <int> mag(s),a(n),b(n),c(n);
   for(int i=0;i<n-1;i++){
      cin>>a[i]>>b[i]>>c[i];
      g[a[i]].pb({b[i],c[i]});
      g[b[i]].pb({a[i],c[i]});
   }
   dfs(e,0);
   
   for(int i=0;i<s;i++){
      cin>>mag[i];
      shop[mag[i]]=1;
   }
   for(int i=1;i<=n;i++){
      dis2[i]=1e18;
   }
   dfs2(e,0);
   for(int i=1;i<=n;i++){
      if(dis2[i]!=1e18)dis2[i]-=2*dis[i];
      
   }
   par[e]=e;
   for(int i=1;i<=n;i++){
      jmp[i][0]=par[i];
      jmp_mn[i][0]=dis2[par[i]];
   }
   for(int j=1;j<20;j++){
      for(int i=1;i<=n;i++){
         jmp[i][j]=jmp[jmp[i][j-1]][j-1];
         jmp_mn[i][j]=min(jmp_mn[i][j-1],jmp_mn[jmp[i][j-1]][j-1]);
      }
   }
   
   while(q--){
      int ind,x;
      cin>>ind>>x;
      ind--;
      int u=a[ind];
      int v=b[ind];
      if(d[u]<d[v])swap(u,v);
      if(lca(u,x)!=u)cout<<"escaped\n";
      else{
         int ans=dis[x],mn=dis2[x];
         for(int i=19;i>=0;i--){
            if(d[jmp[x][i]]>=d[u]){
               mn=min(mn,jmp_mn[x][i]);
               x=jmp[x][i];
            }
         }
         mn=min(mn,dis2[x]);
         if(mn==1e18)cout<<"oo\n";
         else cout<<ans+mn<<"\n";
      }
   }
}
/*

 */

• Subtask 1: 9 / 9
• Subtask 2: 27 / 27
• Subtask 3: 23 / 23
• Subtask 4: 41 / 41