Submission #1007576

#	Time	Username	Problem	Language	Result	Execution time	Memory
1007576		Ludissey	Cat in a tree (BOI17_catinatree)	C++14	0 / 100	0 ms	348 KiB

catinatree

#include <bits/stdc++.h>
#define int long long
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
 
using namespace std;

vector<vector<int>> neigh;
vector<int> dp;
vector<int> visited;
vector<int> center;

int n,d;

pair<int,int> find_furthest(int x, int p){
    pair<int,int> furthest={x,1};
    for (auto u : neigh[x])
    {
        if(u==p) continue;
        pair<int,int> c=find_furthest(u,x);
        c.second++;
        if(furthest.second<c.second) furthest=c;
    }
    dp[x]=furthest.second;
    return furthest;
}

bool find_center(int x, int p, int dist, int dest){
    if(x==dest) return true;
    for (auto u : neigh[x])
    {
        if(u==p) continue;
        bool b=find_center(u,x,dist,dest);
        if(b){
            if(dp[x]==(dist+1)/2||dp[x]==(2+dist)/2) center.push_back(x);
            return true;
        }
    }
    return false;
}

int mark(int x, int p, int res){
    int s=(res==0);
    int nr=res;
    if(nr<=0) nr=d;
    for (auto u : neigh[x])
    {
        if(u==p) continue;
        s+=mark(u,x,nr-1);
    }
    return s;
}

signed main() {
    ios_base::sync_with_stdio(false); cin.tie(nullptr);
    cin >> n >> d;
    dp.resize(n,0);
    visited.resize(n,0);
    neigh.resize(n);

    for (int i = 1; i < n; i++)
    {
        int p; cin >> p;
        neigh[i].push_back(p);
        neigh[p].push_back(i);
    }
    int u=find_furthest(0,-1).first;
    pair<int,int> v=find_furthest(u,-1);

    find_center(u,-1,v.second,v.first);
    int mx=0;
    for (int i = 0; i < sz(center); i++)
    {
        mx=max(mx,mark(center[i],-1,0));
    }
    cout << mx << "\n";
    return 0;
}

• Subtask 1: 0 / 11
• Subtask 2: 0 / 40
• Subtask 3: 0 / 49