Submission #1059541

#	Time	Username	Problem	Language	Result	Execution time	Memory
1059541		shiomusubi496	Thousands Islands (IOI22_islands)	C++17	11.90 / 100	35 ms	16220 KiB

islands

#include "islands.h"

#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define rep2(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rrep(i, n) for (int i = (int)(n) - 1; i >= 0; --i)
#define rrep2(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); --i)

#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)

using namespace std;

using ll = long long;

template<class T, class U> bool chmin(T& a, const U& b) { return a > b ? a = b, true : false; }
template<class T, class U> bool chmax(T& a, const U& b) { return a < b ? a = b, true : false; }

struct edge {
    int to, idx;
};

using Graph = vector<vector<edge>>;

class StronglyConnectedComponents {
    Graph G, RG;
    vector<bool> seen;
    vector<int> ord;
    vector<int> cmp;
    int cnt;

    void dfs1(int v) {
        if (seen[v]) return;
        seen[v] = true;
        for (auto e : G[v]) dfs1(e.to);
        ord.push_back(v);
    }
    void dfs2(int v) {
        if (cmp[v] != -1) return;
        cmp[v] = cnt;
        for (auto e : RG[v]) dfs2(e.to);
    }

public:
    StronglyConnectedComponents(Graph G_, Graph RG_) : G(G_), RG(RG_) {
        seen.assign(G.size(), false);
        rep (i, G.size()) dfs1(i);
        reverse(all(ord));
        cmp.assign(G.size(), -1);
        cnt = 0;
        for (int i : ord) {
            if (cmp[i] == -1) {
                dfs2(i);
                ++cnt;
            }
        }
    }
    vector<vector<int>> get() const {
        vector<vector<int>> res(cnt);
        rep (i, G.size()) res[cmp[i]].push_back(i);
        return res;
    }
};

std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V) {
    Graph G(N), RG(N);
    rep (i, M) {
        G[U[i]].push_back({V[i], i});
        RG[V[i]].push_back({U[i], i});
    }
    vector<int> cnt(N);
    {
        vector<bool> seen(N);
        auto dfs = [&](auto&& self, int v) -> void {
            if (seen[v]) return;
            seen[v] = true;
            if (cnt[v] < 2) {
                ++cnt[v];
                for (auto e : G[v]) self(self, e.to);
            }
            seen[v] = false;
        };
        dfs(dfs, 0);
    }
    auto g = StronglyConnectedComponents(G, RG).get();
    rep (i, g.size()) {
        if (g[i].size() <= 1) continue;
        for (int v : g[i]) {
            if (cnt[v] >= 2) return true;
        }
    }
    return false;
}

• Subtask 1: 1.75 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 0 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 0 / 45