Submission #91843

#	Time	Username	Problem	Language	Result	Execution time	Memory
91843		easrui	Islands (IOI08_islands)	C++14	80 / 100	1368 ms	132096 KiB

islands

#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e6+5;
struct Edge{
    int i,x;
    long long d;
    Edge(){};
    Edge(int a, int b, long long c){i=a;x=b;d=c;};
};

int N;
long long D[MAX],Ans,Len;
bool vE[MAX],vN[MAX],isL[MAX];
vector<Edge> I[MAX];
stack<int> L;
vector<int> Lp;
vector<long long> A,B,C,dis;

void DFS(int i)
{
    if(vN[i]){
        Lp.push_back(i);
        isL[i] = true;
        while(L.top()!=i){
            Lp.push_back(L.top());
            isL[L.top()] = true;
            L.pop();
        }
        return;
    }
    vN[i] = true;
    L.push(i);
    for(auto it : I[i]){
        if(vE[it.i]) continue;
        vE[it.i] = true;
        DFS(it.x);
    }
    if(!L.empty()) L.pop();
}

long long getD(int x, long long d, int r)
{
    long long res=0,tmp=0,subm=0;
    for(auto it : I[x]){
        if(isL[it.x] || it.x==r) continue;
        tmp = getD(it.x,it.d,x);
        if(res<=tmp){
            subm = res;
            res = tmp;
        }
        else subm = max(subm,tmp);
        Len = max(Len,subm+res);
    }
    return res+d;
}

long long getL()
{
    long long res=0,tmp;
    int n = Lp.size();
    Len = 0;
    for(int i=0; i<n; i++)
    {
        for(auto it : I[Lp[i]]){
            if(it.x==Lp[(i+1)%n]) dis.push_back(it.d);
        }
        D[Lp[i]] = getD(Lp[i],0,Lp[i]);
    }
    res = Len;
    A.push_back(D[Lp[0]]);
    for(int i=1; i<n; i++) A.push_back(A[i-1]+D[Lp[i]]-D[Lp[i-1]]+dis[i-1]);
    for(int i=0; i<n; i++) B.push_back(A[i]-D[Lp[i]]*2);
    C.push_back(D[Lp[n-1]]+dis[n-1]);
    for(int i=1; i<n-1; i++) C.push_back(C[i-1]+D[Lp[n-1-i]]-D[Lp[n-i]]+dis[n-1-i]);
    tmp = B[0];
    res = max(res,A[1] - B[0]);
    for(int i=2; i<n; i++){
        tmp = min(tmp,B[i-1]);
        res = max(res,A[i] - tmp);
    }
    tmp = A[0];
    res = max(res,C[n-2] + A[0]);
    for(int i=n-3; i>=0; i--){
        tmp = max(tmp,A[n-2-i]);
        res = max(res,C[i] + tmp);
    }
    return res;
}

int main()
{
    cin >> N;
    for(int i=1; i<=N; i++){
        int x;
        long long d;
        cin >> x >> d;
        I[i].push_back(Edge(i,x,d));
        I[x].push_back(Edge(i,i,d));
    }
    for(int j=1; j<=N; j++){
        if(vN[j]) continue;
        Lp.clear();
        A.clear();
        B.clear();
        C.clear();
        dis.clear();
        DFS(j);
        Ans += getL();
        //cout << Ans;
    }
    cout << Ans;
}


/*8
3 8
7 2
4 2
1 4
1 17
3 4
2 3
1 15
*/

• 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: 0 / 10
• Subtask 9: 0 / 10