Submission #990419

#	Time	Username	Problem	Language	Result	Execution time	Memory
990419		huutuan	Islands (IOI08_islands)	C++14	100 / 100	432 ms	103764 KiB

islands

#include<bits/stdc++.h>

using namespace std;

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

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

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;
   }
   long long ans=0;
   for (int i=1; i<=n; ++i) if (!vis[i]){
      int L=0, R=0;
      long long cur=0;
      int u=i;
      while (1){
         if (_vis[u]) break;
         _vis[u]=1;
         cycle[R++]=u;
         u=par[u];
      }
      L=find(cycle+L, cycle+R, u)-cycle;
      for (int j=L; j<R; ++j) on_cycle[cycle[j]]=1;
      for (int j=L; j<R; ++j){
         dfs(cycle[j]);
         cur=max(cur, f[cycle[j]][1]);
      }
      pf[L]=0;
      for (int j=L; j<R; ++j){
         pf[j+1]=pf[j]+wpar[cycle[j]];
      }
      long long sum=pf[R];
      long long mx1=-1e18, mx2=-1e18;
      for (int j=L; j<R; ++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+=cur;
   }
   cout << ans << '\n';
   return 0;
}

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