Submission #900411

#	Time	Username	Problem	Language	Result	Execution time	Memory
900411		abcvuitunggio	Islands (IOI08_islands)	C++17	90 / 100	797 ms	131072 KiB

islands

#include <bits/stdc++.h>
using namespace std;
const int mxn=1000001;
const long long INF=1e18;
vector <int> ke[mxn],V[mxn],q;
int n,p[mxn],l[mxn],last[mxn],r[mxn];
bitset <mxn> ch;
long long dp[mxn],dp2[mxn],d[mxn],val,res,a,b,sum,s;
pair <long long, int> mx={-1,0},mx2={-1,0};
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){
    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];
    for (int v:ke[u])
        dfs2(v);
}
int f(int i){
    return (r[i]==i?i:r[i]=f(r[i]));
}
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];
        last[p[i]]++;
    }
    iota(r,r+n+1,0);
    for (int i=1;i<=n;i++)
        if (!last[i])
            q.push_back(i);
    while (!q.empty()){
        int u=q.back();
        q.pop_back();
        ch[u]=1;
        ke[p[u]].push_back(u);
        r[f(u)]=f(p[u]);
        if (!--last[p[u]])
            q.push_back(p[u]);
    }
    for (int i=1;i<=n;i++)
        if (f(i)==i){
            dfs(i);
            dfs2(i);
        }
    memset(last,0,sizeof(last));
    for (int i=1;i<=n;i++){
        vector <int>().swap(ke[i]);
        V[f(i)].push_back(i);
    }
    for (int i=1;i<=n;i++){
        if (ch[i])
            continue;
        sum=0,a=-INF,b=-INF;
        int j=i;
        while (true){
            sum+=l[j];
            ch[j]=1;
            last[p[j]]=j;
            j=p[j];
            if (j==i)
                break;
        }
        val=0,s=sum;
        for (int j=last[i];;j=last[j]){
            for (int u:V[j])
                val=max(val,max(dp2[u],d[u]+max(a-s,b+sum+s)));
            a=max(a,dp[j]+s);
            b=max(b,dp[j]-s);
            s-=l[last[j]];
            if (j==i)
                break;
        }
        res+=val;
    }
    cout << res;
}

• 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