Submission #989482

#	Time	Username	Problem	Language	Result	Execution time	Memory
989482		huutuan	Islands (IOI08_islands)	C++14	64 / 100	188 ms	131072 KiB

islands

#include<bits/stdc++.h>

using namespace std;

#define int long long

const int N=1e6+10;
int n, vis[N], par[N], wpar[N], on_cycle[N];
vector<pair<int, int>> g[N];
int pf[N], f[N][2];

void dfs(int u){
   vis[u]=1;
   int mx1=-1e18, mx2=-1e18;
   for (auto &e:g[u]){
      int v=e.first, w=e.second;
      if (on_cycle[v]) continue;
      dfs(v);
      int val=f[v][0]+w;
      f[u][0]=max(f[u][0], val);
      f[u][1]=max(f[u][1], f[v][1]);
      if (mx1<val) mx2=mx1, mx1=val;
      else mx2=max(mx2, mx1);
   }
   f[u][1]=max({f[u][1], f[u][0], mx1+mx2});
}

int32_t main(){
   ios_base::sync_with_stdio(false);
   cin.tie(nullptr);
   cin >> n;
   for (int i=1; i<=n; ++i){
      int j, k; cin >> j >> k;
      g[j].emplace_back(i, k);
      par[i]=j;
      wpar[i]=k;
   }
   vector<int> ans;
   for (int i=1; i<=n; ++i) if (!vis[i]){
      int cur=0;
      vector<int> cycle;
      int u=i;
      while (1){
         if (vis[u]) break;
         vis[u]=1;
         cycle.push_back(u);
         u=par[u];
      }
      cycle.erase(cycle.begin(), find(cycle.begin(), cycle.end(), u));
      for (int v:cycle) on_cycle[v]=1;
      for (int v:cycle){
         dfs(v);
         cur=max(cur, f[v][1]);
      }
      for (int j=1; j<=(int)cycle.size(); ++j){
         pf[j]=pf[j-1]+wpar[cycle[j-1]];
      }
      int sum=pf[(int)cycle.size()];
      int mx1=-1e18, mx2=-1e18;
      for (int j=0; j<(int)cycle.size(); ++j){
         cur=max(cur, f[cycle[j]][0]+pf[j]+mx1);
         cur=max(cur, f[cycle[j]][0]-pf[j]+mx2);
         mx1=max(mx1, f[cycle[j]][0]-pf[j]);
         mx2=max(mx2, f[cycle[j]][0]+sum+pf[j]);
      }
      ans.push_back(cur);
   }
   sort(ans.rbegin(), ans.rend());
   // ans.resize(2, 0);
   // cout << ans[0]+ans[1] << '\n';
   cout << accumulate(ans.begin(), ans.end(), 0ll) << '\n';
   return 0;
}

• Subtask 1: 27 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 0 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10