Submission #823619

#	Time	Username	Problem	Language	Result	Execution time	Memory
823619		finn__	Thousands Islands (IOI22_islands)	C++17	24 / 100	76 ms	19020 KiB

islands

#include <bits/stdc++.h>

#include "islands.h"

using namespace std;

constexpr size_t N_MAX = 100000;

set<pair<int, int>> g[N_MAX];
bitset<N_MAX> visited, in_dfs;

int find_cycle(int u, vector<int> &cycle, vector<int> &path_to_cycle)
{
    if (in_dfs[u])
        return u;
    if (visited[u])
        return -1;

    in_dfs[u] = 1;
    visited[u] = 1;

    for (auto const &[v, i] : g[u])
    {
        int x = find_cycle(v, cycle, path_to_cycle);
        if (x != -1)
        {
            cycle.push_back(i);
            return x == u ? -1 : x;
        }
        else if (!cycle.empty())
        {
            path_to_cycle.push_back(i);
            return -1;
        }
    }

    in_dfs[u] = 0;
    return -1;
}

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V)
{
    for (int i = 0; i < M; ++i)
        g[U[i]].emplace(V[i], i);

    vector<int> cycle, path_to_cycle;
    find_cycle(0, cycle, path_to_cycle);
    if (cycle.empty())
        return false;
    reverse(cycle.begin(), cycle.end());
    reverse(path_to_cycle.begin(), path_to_cycle.end());

    vector<int> tour = path_to_cycle;
    tour.insert(tour.end(), cycle.begin(), cycle.end());
    for (size_t i = path_to_cycle.size(); i < path_to_cycle.size() + cycle.size(); ++i)
    {
        if (tour[i] + 1 < M && U[tour[i]] == U[tour[i] + 1] && V[tour[i]] == V[tour[i] + 1])
            tour.push_back(tour[i] + 1);
        else
            tour.push_back(tour[i] - 1);
    }

    tour.resize(tour.size() * 2);
    copy(tour.begin() + path_to_cycle.size(), tour.begin() + tour.size() / 2, tour.begin() + tour.size() / 2);
    copy(path_to_cycle.begin(), path_to_cycle.end(), tour.end() - path_to_cycle.size());
    reverse(tour.begin() + tour.size() / 2, tour.begin() + tour.size() / 2 + cycle.size());
    reverse(tour.begin() + tour.size() / 2 + cycle.size(), tour.end() - path_to_cycle.size());
    reverse(tour.end() - path_to_cycle.size(), tour.end());

    return tour;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 5
• Subtask 3: 0 / 21
• Subtask 4: 24 / 24
• Subtask 5: 0 / 45