Submission #799284

#	Time	Username	Problem	Language	Result	Execution time	Memory
799284		finn__	Newspapers (CEOI21_newspapers)	C++17	100 / 100	3 ms	468 KiB

newspapers

#include <bits/stdc++.h>
using namespace std;

constexpr size_t N = 1000;

vector<size_t> g[N];

pair<size_t, size_t> find_farthest(size_t u, size_t p = -1)
{
    size_t x = u, y = 0;
    for (size_t const &v : g[u])
        if (v != p)
        {
            auto [w, d] = find_farthest(v, u);
            if (d > y)
                x = w, y = d;
        }
    return {x, y + 1};
}

bool find_path(size_t dest, vector<size_t> &path, size_t u, size_t p = -1)
{
    if (u == dest)
    {
        path.push_back(u);
        return 1;
    }

    for (size_t const &v : g[u])
        if (v != p)
        {
            if (find_path(dest, path, v, u))
            {
                path.push_back(u);
                return 1;
            }
        }

    return 0;
}

vector<size_t> find_diameter()
{
    auto [u, _] = find_farthest(0);
    auto [v, d] = find_farthest(u);
    vector<size_t> diameter;
    find_path(v, diameter, u);
    return diameter;
}

void walk_diameter(vector<size_t> const &diameter, vector<size_t> &a)
{
    for (size_t i = 1; i < diameter.size() - 1; ++i)
    {
        size_t u = diameter[i];
        a.push_back(u);
        for (size_t v : g[u])
            if (g[v].size() != 1 && find(diameter.begin(), diameter.end(), v) == diameter.end())
                a.push_back(v), a.push_back(u);
    }
}

int main()
{
    size_t n, m;
    cin >> n >> m;

    if (m != n - 1)
    {
        cout << "NO\n";
        return 0;
    }
    if (n == 1)
    {
        cout << "YES\n1\n1\n";
        return 0;
    }
    if (n == 2)
    {
        cout << "YES\n2\n1 1\n";
        return 0;
    }

    for (size_t i = 0; i < m; ++i)
    {
        size_t u, v;
        cin >> u >> v;
        g[u - 1].push_back(v - 1);
        g[v - 1].push_back(u - 1);
    }

    vector<size_t> diameter = find_diameter();
    for (size_t i = 0; i < n; ++i)
        if (g[i].size() != 1)
        {
            bool can_escape = find(diameter.begin(), diameter.end(), i) == diameter.end();
            for (size_t v : g[i])
                can_escape &= find(diameter.begin(), diameter.end(), v) == diameter.end();
            if (can_escape)
            {
                cout << "NO\n";
                return 0;
            }
        }

    cout << "YES\n";
    vector<size_t> a;

    walk_diameter(diameter, a);
    reverse(diameter.begin(), diameter.end());
    walk_diameter(diameter, a);

    cout << a.size() << '\n';
    for (size_t u : a)
        cout << u + 1 << ' ';
    cout << '\n';
}

• Subtask 1: 12 / 12
• Subtask 2: 8 / 8
• Subtask 3: 80 / 80