Submission #615419

#	Time	Username	Problem	Language	Result	Execution time	Memory
615419		KoD	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	430 ms	59920 KiB

mousetrap

#include <bits/stdc++.h>

using std::vector;

template <class F> struct fixed : private F {
    explicit fixed(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;
    vector<vector<int>> graph(N);
    for (int e = 1; e < N; ++e) {
        int a, b;
        std::cin >> a >> b;
        a -= 1, b -= 1;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    vector<int> parent(N);
    parent[T] = -1;
    fixed([&](auto&& dfs, const int u) -> void {
        for (const int v : graph[u]) {
            if (v != parent[u]) {
                parent[v] = u;
                dfs(v);
            }
        }
    })(T);
    vector<int> path;
    vector<char> on_path(N);
    for (int u = M; u != T; u = parent[u]) {
        path.push_back(u);
        on_path[u] = true;
    }
    const int L = (int)path.size();
    vector<vector<int>> dp(L);
    for (int i = 0; i < L; ++i) {
        for (const int src : graph[path[i]]) {
            if (!on_path[src]) {
                dp[i].push_back(fixed([&](auto&& dfs, const int u) -> int {
                    vector<int> list;
                    for (const int v : graph[u]) {
                        if (v != parent[u]) {
                            list.push_back(dfs(v));
                        }
                    }
                    const int n = (int)list.size();
                    std::sort(list.rbegin(), list.rend());
                    return (n >= 2 ? list[1] : 0) + n;
                })(src));
            }
        }
    }
    vector<int> above(L);
    for (int i = L - 1; i > 0; --i) {
        above[i - 1] = above[i] + (int)graph[path[i]].size() - 2;
    }
    const auto check = [&](const int thres) {
        int cut = 0;
        for (int i = 0; i < L; ++i) {
            const int offset = cut + above[i] + (int)dp[i].size();
            for (const int x : dp[i]) {
                if (offset + x > thres) {
                    if (cut > i) {
                        return false;
                    }
                    cut += 1;
                }
            }
        }
        return cut <= thres;
    };
    int ok = N, ng = -1;
    while (ok - ng > 1) {
        const int md = (ok + ng) / 2;
        (check(md) ? ok : ng) = md;
    }
    std::cout << ok << '\n';
    return 0;
}

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