Submission #1215148

#	Time	Username	Problem	Language	Result	Execution time	Memory
1215148		madamadam3	Cat in a tree (BOI17_catinatree)	C++20	51 / 100	1098 ms	14592 KiB

catinatree

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N, D;
    if (!(cin >> N >> D)) return 0;

    vector<vector<int>> adj(N);
    for (int i = 1; i < N; ++i) {
        int x;                  // parent of i
        cin >> x;
        adj[i].push_back(x);
        adj[x].push_back(i);
    }

    if (D == 1) {              
        cout << N << '\n';
        return 0;
    }

    vector<int> depth(N, 0), parent(N, -1);
    {
        vector<int> st = {0};
        parent[0] = -2;         
        while (!st.empty()) {
            int u = st.back(); st.pop_back();
            for (int v : adj[u]) if (v != parent[u]) {
                parent[v] = u;
                depth[v]  = depth[u] + 1;
                st.push_back(v);
            }
        }
    }

    int maxDepth = *max_element(depth.begin(), depth.end());
    vector<vector<int>> byDepth(maxDepth + 1);
    for (int v = 0; v < N; ++v)
        byDepth[ depth[v] ].push_back(v);

    vector<char> blocked(N, 0);  
    vector<int>  seen(N, 0);        
    int stamp = 1;

    int answer = 0;
    queue<pair<int,int>> q;      

    for (int d = maxDepth; d >= 0; --d) {
        for (int v : byDepth[d]) {
            if (blocked[v]) continue;   

            ++answer;              
            blocked[v] = 1;

            q.push({v, 0});
            seen[v] = stamp;

            while (!q.empty()) {
                auto [u, dist] = q.front();
                q.pop();

                if (dist + 1 >= D) continue;   

                for (int w : adj[u]) {
                    if (seen[w] == stamp) continue; 
                    seen[w] = stamp;

                    blocked[w] = 1;    
                    q.push({w, dist + 1});
                }
            }
            ++stamp;                  
        }
    }

    cout << answer << '\n';
    return 0;
}

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