Submission #900359

#	Time	Username	Problem	Language	Result	Execution time	Memory
900359		abcvuitunggio	Islands (IOI08_islands)	C++17	70 / 100	351 ms	131072 KiB

islands

#include <bits/stdc++.h>
using namespace std;
const int mxn=1000001;
const long long INF=1e18;
vector <int> ke[mxn],ve[mxn],V[mxn],tmp;
vector <long long> s;
int n,p[mxn],l[mxn],vis[mxn],vis2[mxn],root[mxn],cycle[mxn],idx;
long long dp[mxn],dp2[mxn],d[mxn],mx,res;
void dfs(int u){
    for (int v:ke[u]){
        d[v]=d[u]+l[v];
        dfs(v);
        dp[u]=max(dp[u],dp[v]+l[v]);
    }
}
void dfs2(int u){
    pair <long long, int> mx={-1,0},mx2={-1,0};
    for (int v:ke[u]){
        auto tmp=make_pair(dp[v]+l[v],v);
        if (tmp>mx){
            mx2=mx;
            mx=tmp;
        }
        else
            mx2=max(mx2,tmp);
    }
    for (int v:ke[u]){
        dp2[v]=max(dp2[u],(mx.second==v?mx2.first:mx.first))+l[v];
        dfs2(v);
    }
}
int main(){
    ios_base::sync_with_stdio(NULL);cin.tie(nullptr);
    cin >> n;
    for (int i=1;i<=n;i++)
        cin >> p[i] >> l[i];
    for (int i=1;i<=n;i++)
        if (!vis[i]){
            int j=i;
            tmp.clear();
            while (true){
                tmp.push_back(i);
                vis2[i]=tmp.size();
                i=p[i];
                if (vis[i]){
                    for (int j:tmp){
                        root[j]=root[i];
                        cycle[j]=cycle[i];
                        ke[p[j]].push_back(j);
                        vis[j]=1;
                    }
                    break;
                }
                if (vis2[i]){
                    for (int j=vis2[i]-1;j<tmp.size();j++){
                        root[tmp[j]]=tmp[j];
                        cycle[tmp[j]]=idx;
                        ve[idx].push_back(tmp[j]);
                    }
                    for (int j=0;j<vis2[i]-1;j++){
                        root[tmp[j]]=i;
                        ke[tmp[j+1]].push_back(tmp[j]);
                    }
                    for (int j:tmp){
                        cycle[j]=cycle[i];
                        vis[j]=1;
                    }
                    idx++;
                    break;
                }
            }
            i=j;
        }
    for (int i=1;i<=n;i++)
        if (root[i]==i){
            dfs(i);
            dfs2(i);
        }
    for (int i=1;i<=n;i++)
        V[root[i]].push_back(i);
    for (int i=0;i<idx;i++){
        int sz=ve[i].size();
        long long a=-INF,b=-INF;
        for (int j=0;j<sz;j++)
            s.push_back((s.empty()?0:s.back())+l[ve[i][(j?j:sz)-1]]);
        mx=0;
        for (int j=sz-1;j>=0;j--){
            for (int u:V[ve[i][j]]){
                long long val=max(max(dp[u],dp2[u]),d[u]+max(a-s[j],b+s.back()+s[j]));
                mx=max(mx,val);
            }
            a=max(a,dp[ve[i][j]]+s[j]);
            b=max(b,dp[ve[i][j]]-s[j]);
        }
        s.clear();
        res+=mx;
    }
    cout << res;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:55:43: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   55 |                     for (int j=vis2[i]-1;j<tmp.size();j++){
      |                                          ~^~~~~~~~~~~

• 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: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10