Submission #434859

#	Time	Username	Problem	Language	Result	Execution time	Memory
434859		KoD	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	1337 ms	69456 KiB

mousetrap

#include <bits/stdc++.h>

template <class T> using Vec = std::vector<T>;

template <class F> struct RecLambda : private F {
    explicit RecLambda(F&& f) : F(std::forward<F>(f)) {}
    template <class... Args> decltype(auto) operator() (Args&&... args) const {
        return F::operator()(*this, std::forward<Args>(args)...);
    }
};

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int N, T, M;
    std::cin >> N >> T >> M;
    T -= 1;
    M -= 1;
    Vec<Vec<int>> graph(N);
    for (int i = 0; i < N - 1; ++i) {
        int a, b;
        std::cin >> a >> b;
        a -= 1;
        b -= 1;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    Vec<int> parent(N, -1);
    RecLambda([&](auto&& dfs, const int u) -> void {
        for (const int v : graph[u]) {
            if (parent[u] != v) {
                parent[v] = u;
                dfs(v);
            }
        }
    })(T);
    Vec<int> path;
    Vec<char> on_path(N);
    for (int u = M; u != T; u = parent[u]) {
        path.push_back(u);
        on_path[u] = true;
    }
    Vec<int> dp(N, -1);
    const auto down = RecLambda([&](auto&& dfs, const int u) -> int {
        if (dp[u] != -1) {
            return dp[u];
        }
        Vec<int> cand;
        for (const int v : graph[u]) {
            if (v != parent[u] and !on_path[v]) {
                cand.push_back(dfs(v));
            }
        } 
        std::sort(cand.rbegin(), cand.rend());
        if (cand.size() <= 1) {
            return dp[u] = (int) cand.size();
        }
        return dp[u] = cand[1] + (int) cand.size();
    });
    Vec<int> cut(N);
    RecLambda([&](auto&& dfs, const int u) -> void {
        for (const int v : graph[u]) {
            if (parent[u] != v) {
                cut[v] += cut[u];
                if (u != T) {
                    cut[v] += (int) graph[u].size() - 2;
                }
                dfs(v);
            }
        }
    })(T);
    int ok = N, ng = (int) path.size();
    while (ok - ng > 1) {
        const int md = (ok + ng) / 2;
        ([&] {
            for (int i = 0; i < (int) path.size(); ++i) {
                const int u = path[i];
                if (down(u) + cut[u] + i > md) {
                    return false;
                }
            }
            return true;
        }() ? ok : ng) = md;
    }
    std::cout << ok << '\n';
    return 0;
}

• Subtask 1: 0 / 20
• Subtask 2: 25 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35