Submission #1019796

#	Time	Username	Problem	Language	Result	Execution time	Memory
1019796		ttamx	Islands (IOI08_islands)	C++17	90 / 100	490 ms	131072 KiB

islands

#include<bits/stdc++.h>

using namespace std;

using ll = long long;

const int N=1e6+5;

int n;
pair<int,int> nxt[N];
int deg[N];
queue<int> q;
vector<pair<int,int>> adj[N];
ll dp[N];
ll dia,ans;

void dfs(int u){
    ll mx=0,mx2=0;
    for(auto [v,w]:adj[u]){
        dfs(v);
        mx2=max(mx2,dp[v]+w);
        if(mx<mx2)swap(mx,mx2);
    }
    dp[u]=mx;
    dia=max(dia,mx+mx2);
}

int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    cin >> n;
    for(int i=1;i<=n;i++){
        auto &[v,w]=nxt[i];
        cin >> v >> w;
        deg[v]++;
    }
    for(int i=1;i<=n;i++)if(!deg[i])q.emplace(i);
    while(!q.empty()){
        int u=q.front();
        q.pop();
        auto [v,w]=nxt[u];
        adj[v].emplace_back(u,w);
        if(--deg[v]==0)q.emplace(v);
    }
    for(int i=1;i<=n;i++)if(deg[i]){
        ll len=0;
        vector<pair<int,ll>> comp;
        for(int u=i;deg[u];){
            comp.emplace_back(u,len);
            deg[u]=0;
            auto [v,w]=nxt[u];
            len+=w;
            u=v;
        }
        int m=comp.size();
        dia=0;
        for(auto [u,w]:comp)dfs(u);
        deque<pair<ll,int>> dq;
        for(auto [u,w]:comp){
            ll val=dp[u]-w;
            while(!dq.empty()&&dq.back().first<val)dq.pop_back();
            dq.emplace_back(val,u);
        }
        for(auto [u,w]:comp){
            if(!dq.empty()&&dq.front().second==u)dq.pop_front();
            if(!dq.empty())dia=max(dia,w+len+dp[u]+dq.front().first);
            ll val=dp[u]-w-len;
            while(!dq.empty()&&dq.back().first<val)dq.pop_back();
            dq.emplace_back(val,u);
        }
        ans+=dia;
    }
    cout << ans;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:54:13: warning: unused variable 'm' [-Wunused-variable]
   54 |         int m=comp.size();
      |             ^

• 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: 0 / 10