Submission #900434

#	Time	Username	Problem	Language	Result	Execution time	Memory
900434		abcvuitunggio	Islands (IOI08_islands)	C++17	90 / 100	647 ms	131072 KiB

islands

#include <iostream>
#include <bitset>
#include <vector>
#include <queue>
using namespace std;
const int mxn=1000001;
const long long INF=1e18;
vector <int> ke[mxn];
queue <int> q;
int n,p[mxn],l[mxn],last[mxn],r[mxn],x,u;
bitset <mxn> ch;
long long dp[mxn],d[mxn],val,res,a,b,sum,s;
int dfs(int u){
    int mx=u;
    for (int v:ke[u]){
        int w=dfs(v);
        if (dp[v]+l[v]>dp[u])
            mx=w;
        dp[u]=max(dp[u],dp[v]+l[v]);
    }
    return mx;
}
long long dfs2(int u, int par){
    long long mx=0;
    for (int v:ke[u])
        if (v!=par)
            mx=max(mx,dfs2(v,u)+l[v]);
    if (ch[u]&&p[u]!=par)
        mx=max(mx,dfs2(p[u],u)+l[u]);
    return mx;
}
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]]++;
        r[i]=i;
    }
    for (int i=1;i<=n;i++)
        if (!last[i])
            q.push(i);
    while (!q.empty()){
        u=q.front();
        q.pop();
        ch[u]=1;
        r[f(u)]=f(p[u]);
        if (!--last[p[u]])
            q.push(p[u]);
    }
    for (int i=1;i<=n;i++)
        if (ch[i])
            ke[p[i]].push_back(i);
    for (int i=1;i<=n;i++)
        if (!ch[i])
            d[i]=dfs2(dfs(i),0);
    for (int i=1;i<=n;i++){
        last[i]=0;
        vector <int>().swap(ke[i]);
    }
    for (int i=1;i<=n;i++){
        if (ch[i])
            continue;
        sum=0,a=-INF,b=-INF;
        x=i;
        while (true){
            sum+=l[x];
            ch[x]=1;
            last[p[x]]=x;
            x=p[x];
            if (x==i)
                break;
        }
        val=0,s=sum;
        for (x=last[i];;x=last[x]){
            val=max(max(val,d[x]),dp[x]+max(a-s,b+sum+s));
            a=max(a,dp[x]+s);
            b=max(b,dp[x]-s);
            s-=l[last[x]];
            if (x==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