Submission #1097032

#	Time	Username	Problem	Language	Result	Execution time	Memory
1097032		vlad1_1	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	201 ms	80692 KiB

mousetrap

#include <bits/stdc++.h>
// https://oj.uz/problem/view/CEOI17_mousetrap


using namespace std;

void dfs(int node, int parent, vector<vector<int>>& graph, vector<int>& parents, vector<vector<int>>& depths, int depth = 0) {
    if (depths.size() <= depth) {
        depths.resize(4 * (depth + 1));
    }
    depths[depth].push_back(node);

    for (int child : graph[node]) {
        if (child == parent) continue;
        parents[child] = node;
        dfs(child, node, graph, parents, depths, depth + 1);
    }
}

auto max2(const vector<int>& adjacent, const vector<int>& dp, int parent) {
    if (adjacent.size() < 2)
        return 0;

    auto it = adjacent.cbegin();
    auto sentinel = adjacent.cend();

    if (dp[*it] == parent) {
        it++;
    }
    auto max1 = dp[*it++];
    if (it == sentinel || dp[*it] == parent) {
        it++;
    }
    if (!(it < sentinel)) {
        return 0;
    }
    auto max2 = dp[*it++];

    if (max1 < max2) {
        swap(max1, max2);
    }

    for (; it < sentinel; it++) {
        if (dp[*it] == parent) {
            continue;
        }
        if (dp[*it] > max1) {
            max2 = max1;
            max1 = dp[*it];
        } else if (dp[*it] > max2) {
            max2 = dp[*it];
        }
    }

    return max2;
}

int main() {
    int n, t, m;

    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> n >> t >> m;

    vector<vector<int>> graph(n+1);
    for (int i = 1; i < n; i++) {
        int x, y;
        cin >> x >> y;
        graph[x].push_back(y);
        graph[y].push_back(x);
    }
    assert(find(graph[t].begin(), graph[t].end(), m) != graph[t].end());
    graph[t] = {m};
    
    vector<int> parents(n+1);
    vector<vector<int>> depths;
    parents[t] = 0;
    dfs(t, 0, graph, parents, depths);

    vector<int> dp(n+1);
    for (int depth = depths.size() - 1; depth >= 0; depth--) {
        auto& row = depths[depth];
        for (int node : row) {
            dp[node] = graph[node].size() + max2(graph[node], dp, parents[node]);
        }
    }

    cout << dp[m] << '\n';
}

Compilation message (stderr)

mousetrap.cpp: In function 'void dfs(int, int, std::vector<std::vector<int> >&, std::vector<int>&, std::vector<std::vector<int> >&, int)':
mousetrap.cpp:8:23: warning: comparison of integer expressions of different signedness: 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
    8 |     if (depths.size() <= depth) {
      |         ~~~~~~~~~~~~~~^~~~~~~~

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