Submission #856023

#	Time	Username	Problem	Language	Result	Execution time	Memory
856023		Cyanmond	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	744 ms	72316 KiB

mousetrap

#include <bits/stdc++.h>

using namespace std;

#define rep(i, l, r) for (int i = (l); i < (r); ++i)
#define per(i, l, r) for (int i = (r - 1); i >= l; --i)
#define ALL(x) (x).begin(), (x).end()

using i64 = long long;

void main_() {
    int N, T, M;
    cin >> N >> T >> M;
    --T, --M;
    if (T == M) {
        cout << 0 << endl;
        return;
    }

    vector<int> A(N - 1), B(N - 1);
    vector<vector<int>> Tree(N);
    rep(i, 0, N - 1) {
        cin >> A[i] >> B[i];
        Tree[--A[i]].push_back(--B[i]);
        Tree[B[i]].push_back(A[i]);
    }

    vector<bool> isPath(N);
    vector<int> path;
    auto dfs = [&](auto &&self, const int v, const int p) -> bool {
        bool ret = false;
        for (const int t : Tree[v]) {
            if (t == p) continue;
            ret |= self(self, t, v);
        }
        if (v == T) ret = true;
        isPath[v] = ret;
        if (ret) path.push_back(v);
        return ret;
    };
    dfs(dfs, M, -1);
    reverse(ALL(path));

    vector<i64> dp(N);
    auto dfs2 = [&](auto &&self, const int v, const int p) -> i64 {
        vector<int> vals;
        for (const int t : Tree[v]) {
            if (t == p) continue;
            if (isPath[t]) continue;
            vals.push_back(self(self, t, v));
        }
        sort(ALL(vals), greater());
        i64 cost = -1;
        if (vals.empty()) cost = 0;
        else if (vals.size() == 1) cost = 1;
        else cost = vals[1] + (int)(vals.size()) - 1;
        dp[v] = cost;
        return dp[v] + 1;
    };

    i64 ans = 0;
    bool isOk = false;
    for (const auto e : path) {
        if (e == T) continue;
        if (isOk) {
            ans += (int)Tree[e].size() - 2;
        } else {
            int cnt = (int)Tree[e].size() - 1 - (e == M ? 0 : 1);
            if (cnt >= 1) {
                ans += dfs2(dfs2, e, -1) - 1;
                isOk = true;
            }
        }
    }

    cout << ans << endl;
}

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

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