Submission #923973

#	Time	Username	Problem	Language	Result	Execution time	Memory
923973		Arp	Dreaming (IOI13_dreaming)	C++17	100 / 100	55 ms	17344 KiB

dreaming

#include<bits/stdc++.h>
#include "dreaming.h"
using namespace std;
 
const int N = 1e5;
const int inf = 2e9;
vector<pair<int,int>> adj[N];
int down[N],up[N];
bool vis[N];
 
void dfs(int u){
  vis[u] = true;
  vector<pair<int,int>> all;
  for(auto [v,w] : adj[u]){
    if(vis[v]) continue;
    dfs(v);
    all.emplace_back(v,w);
  }
  int maxi = -inf;
  for(auto [v,w] : all){
    up[v] = max(up[v],maxi + w);
    maxi = max(maxi,down[v] + w);
  }
  reverse(all.begin(),all.end());
  maxi = -inf;
  for(auto [v,w] : all){
    up[v] = max(up[v],maxi + w);
    maxi = max(maxi,down[v] + w);
    down[u] = maxi;
  }
}
int mini = inf;
void dfs2(int u,int p){
  for(auto[v,w] : adj[u]){
    if(v == p) continue;
    up[v] = max(up[v],up[u] + w);
    dfs2(v,u);
  }
  mini = min(mini,max(down[u],up[u]));
}
 
int travelTime(int N,int M,int L,int A[],int B[],int T[]){
  for(int i = 0;i<N;i++){
    up[i] = down[i] = 0;
    vis[i] = false;
  }
  for(int i = 0;i<M;i++){
    adj[A[i]].emplace_back(B[i],T[i]);
    adj[B[i]].emplace_back(A[i],T[i]);
  }
  vector<int> arr;
  int ans = 0;
  int cc = 0;
  for(int i = 0;i<N;i++){
    if(!vis[i]){
      mini = inf;
      dfs(i);
      dfs2(i,-1);
      arr.push_back(mini);
      cc ++;
    }
    ans = max(ans,up[i]);
  }
  assert(cc - 1 == N - M - 1);
  sort(arr.begin(),arr.end());
  int tot = inf;
  if(arr.size() == 1){
    return ans;
  }
  if(arr.size() == 2){
    return max(ans,arr[0] + arr[1] + L);
  }else if(arr.size() > 2){
    int a = arr[arr.size() - 3];
    int b = arr[arr.size() - 2];
    int c = arr[arr.size() - 1];
    tot = min(tot,max(b + c + L,a + c + 2 * L));
    tot = min(tot,max(b + c + L,a + b + 2 * L));
  }
  return max(tot,ans);
}

• Subtask 1: 14 / 14
• Subtask 2: 10 / 10
• Subtask 3: 23 / 23
• Subtask 4: 18 / 18
• Subtask 5: 12 / 12
• Subtask 6: 23 / 23