Submission #533283

#	Time	Username	Problem	Language	Result	Execution time	Memory
533283		KoD	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	345 ms	59228 KiB

mousetrap

#include <bits/stdc++.h>

using std::vector;
using std::array;
using std::pair;
using std::tuple;

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;
    vector<vector<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);
    }
    vector<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);
            }
        }
    })(M);
    vector<int> path;
    for (int u = T; u != M;) {
        path.push_back(u = parent[u]);
    }
    const int L = path.size();
    vector<int> above(L);
    for (int i = 0; i < L - 1; ++i) {
        above[i + 1] = above[i] + (int)graph[path[i]].size() - 2;
    }
    vector<vector<int>> dp(L);
    for (int i = 0, last = T; i < L; ++i) {
        const int cur = path[i];
        for (const int c : graph[cur]) {
            if (c != parent[cur] and c != last) {
                dp[i].push_back(RecLambda([&](auto&& dfs, const int u, const int p) -> int {
                    vector<int> cand;
                    for (const int v : graph[u]) {
                        if (v != p) {
                            cand.push_back(dfs(v, u));
                        }
                    }
                    std::sort(cand.rbegin(), cand.rend());
                    const int size = (int)cand.size();
                    return size + (size <= 1 ? 0 : cand[1]);
                })(c, cur));
            }
        }
        last = cur;
    }
    const auto check = [&](const int thres) {
        int sofar = 0;
        for (int i = L - 1; i >= 0; --i) {
            for (const int c : dp[i]) {
                if (c + above[i] + sofar > thres) {
                    if (sofar > (L - i - 1)) {
                        return false;
                    }
                    sofar += 1;
                }
            }
        }
        return sofar <= 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