Submission #628804

#	Time	Username	Problem	Language	Result	Execution time	Memory
628804		dqhungdl	Thousands Islands (IOI22_islands)	C++17	41.35 / 100	74 ms	33524 KiB

islands

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

const int MAX = 1e5 + 5;
typedef pair<int, int> ii;
int N, mark[MAX];
vector<vector<vector<int>>> g;
vector<ii> ng[MAX];
vector<int> path;

bool dfs(int u) {
    if (mark[u] == 2)
        return false;
    if (mark[u] == 1) {
        path.push_back(u);
        return true;
    }
    mark[u] = 1;
    for (auto &[v, id]: ng[u])
        if (dfs(v)) {
            path.push_back(u);
            return true;
        }
    mark[u] = 2;
    return false;
}

bool dfs1(int u) {
    if ((!u && ng[u].size() >= 2) || ng[u].size() >= 3) {
        path.push_back(u);
        return true;
    }
    if (mark[u])
        return false;
    mark[u] = true;
    for (auto &[v, id]: ng[u])
        if (dfs1(v)) {
            path.push_back(u);
            return true;
        }
    return false;
}

variant<bool, vector<int>> find_journey(int _N, int M, vector<int> U, vector<int> V) {
    N = _N;
    if (N == 2) {
        vector<int> g[2];
        for (int i = 0; i < M; i++)
            g[U[i]].push_back(i);
        if (g[0].size() < 2 || g[1].empty())
            return false;
        return vector<int>({g[0][0], g[1][0], g[0][1], g[0][0], g[1][0], g[0][1]});
    }

    g.resize(N, vector<vector<int>>(N));
    for (int i = 0; i < M; i++)
        g[U[i]][V[i]].push_back(i);
    bool isClique = true;
    for (int i = 0; i < N && isClique; i++)
        for (int j = 0; j < N && isClique; j++)
            if (i != j && g[i][j].empty())
                isClique = false;
    if (isClique)
        return vector<int>({g[0][1][0], g[1][2][0], g[2][0][0], g[0][2][0], g[2][1][0], g[1][0][0],
                            g[2][0][0], g[1][2][0], g[0][1][0], g[1][0][0], g[2][1][0], g[0][2][0]});

    bool isDoubled = M % 2 == 0;
    for (int i = 1; i < M && isDoubled; i += 2)
        if (U[i - 1] != U[i] || V[i - 1] != V[i])
            isDoubled = false;
    if (isDoubled) {
        for (int i = 1; i < M; i += 2)
            ng[U[i]].emplace_back(V[i], i);
        if (dfs(0)) {
            reverse(path.begin(), path.end());
            int pivot = -1;
            for (int i = 0; i < path.size(); i++)
                if (path[i] == path.back()) {
                    pivot = i;
                    break;
                }
            vector<int> rs;
            for (int i = 0; i < pivot; i++)
                rs.push_back(g[path[i]][path[i + 1]][0]);
            for (int i = pivot; i < path.size() - 1; i++)
                rs.push_back(g[path[i]][path[i + 1]][0]);
            for (int i = pivot; i < path.size() - 1; i++)
                rs.push_back(g[path[i]][path[i + 1]][1]);
            for (int i = path.size() - 2; i >= pivot; i--)
                rs.push_back(g[path[i]][path[i + 1]][0]);
            for (int i = path.size() - 2; i >= pivot; i--)
                rs.push_back(g[path[i]][path[i + 1]][1]);
            for (int i = pivot - 1; i >= 0; i--)
                rs.push_back(g[path[i]][path[i + 1]][0]);
            return rs;
        }
        return false;
    }
    for (int i = 0; i < M; i++)
        ng[U[i]].emplace_back(V[i], i);
    if (dfs1(0)) {
        vector<int> rs;
        for (int i = 0; i < path.size() - 1; i++)
            rs.push_back(g[path[i]][path[i + 1]][0]);
        int p = path.size() == 1 ? -1 : path[path.size() - 2];
        vector<int> sample;
        for (auto &[v, id]: ng[path.back()])
            if (v != p) {
                sample.push_back(id);
                if (sample.size() == 2)
                    break;
            }
        for (int id: sample) {
            rs.push_back(id);
            rs.push_back(id % 2 ? id - 1 : id + 1);
        }
        for (int id: sample) {
            rs.push_back(id % 2 ? id - 1 : id + 1);
            rs.push_back(id);
        }
        for (int i = (int) path.size() - 2; i >= 0; i--)
            rs.push_back(g[path[i]][path[i + 1]][0]);
        return rs;
    }
    return false;
}

//int main() {
//    freopen("../_input", "r", stdin);
//    int N, M;
//    assert(2 == scanf("%d %d", &N, &M));
//
//    vector<int> U(M), V(M);
//    for (int i = 0; i < M; ++i) {
//        assert(2 == scanf("%d %d", &U[i], &V[i]));
//    }
//
//    variant<bool, vector<int>> result = find_journey(N, M, U, V);
//    if (result.index() == 0) {
//        printf("0\n");
//        if (get<bool>(result)) {
//            printf("1\n");
//        } else {
//            printf("0\n");
//        }
//    } else {
//        printf("1\n");
//        vector<int> &canoes = get<vector<int>>(result);
//        printf("%d\n", static_cast<int>(canoes.size()));
//        for (int i = 0; i < static_cast<int>(canoes.size()); ++i) {
//            if (i > 0) {
//                printf(" ");
//            }
//            printf("%d", canoes[i]);
//        }
//        printf("\n");
//    }
//    return 0;
//}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:79:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   79 |             for (int i = 0; i < path.size(); i++)
      |                             ~~^~~~~~~~~~~~~
islands.cpp:87:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   87 |             for (int i = pivot; i < path.size() - 1; i++)
      |                                 ~~^~~~~~~~~~~~~~~~~
islands.cpp:89:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   89 |             for (int i = pivot; i < path.size() - 1; i++)
      |                                 ~~^~~~~~~~~~~~~~~~~
islands.cpp:105:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  105 |         for (int i = 0; i < path.size() - 1; i++)
      |                         ~~^~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 24 / 24
• Subtask 5: 0 / 45