Submission #633215

#	Time	Username	Problem	Language	Result	Execution time	Memory
633215		tutis	Thousands Islands (IOI22_islands)	C++17	38.25 / 100	171 ms	17608 KiB

islands

#include "islands.h"

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

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
    int s = 0;
    vector<bool> e(N, true);
    vector<int>ans0;
    {
        vector<int> C(N, 0);
        vector<int>b[N];
        vector<int>ff[N];
        for (int i = 0; i < M; i++)
        {
            C[U[i]]++;
            b[V[i]].push_back(U[i]);
            ff[U[i]].push_back(i);
        }
        stack<int>Q;
        for (int i = 0; i < N; i++)
            if (C[i] == 0)
                Q.push(i);
        while (e[s])
        {
            if (C[s] == 1)
            {
                int s_ = -1;
                for (int ee : ff[s])
                {
                    if (e[V[ee]])
                    {
                        ans0.push_back(ee);
                        s_ = V[ee];
                    }
                }
                for (int t : b[s])
                {
                    if (e[t])
                    {
                        C[t]--;
                        if (C[t] == 0)
                            Q.push(t);
                    }
                }
                e[s] = false;
                s = s_;
                continue;
            }
            if (Q.empty())
                break;
            int a = Q.top();
            Q.pop();
            if (!e[a])
                continue;
            e[a] = false;
            for (int t : b[a])
            {
                if (e[t])
                {
                    C[t]--;
                    if (C[t] == 0)
                        Q.push(t);
                }
            }
        }
        if (!e[s])
            return false;
    }
    vector<int>adj[N];
    for (int i = 0; i < M; i++)
        if (e[U[i]] && e[V[i]])
            adj[U[i]].push_back(i);
    auto c = [&](int s)->pair<vector<int>, vector<int>>
    {
        vector<int> D(N, -1);
        D[s] = 0;
        int t = V[adj[s][0]];
        vector<int>v = {adj[s][0]};
        int val = 0;
        while (D[t] == -1)
        {
            val++;
            D[t] = val;
            v.push_back(adj[t][0]);
            t = V[adj[t][0]];
        }
        vector<int>a, b;
        for (int i = 0; i < D[t]; i++)
            a.push_back(v[i]);
        for (int i = D[t]; i < (int)v.size(); i++)
            b.push_back(v[i]);
        return {a, b};
    };
    pair<vector<int>, vector<int>>c0 = c(s);
    adj[s][0] = adj[s].back();
    pair<vector<int>, vector<int>>c1 = c(s);
    vector<int> ret;
    for (int i : ans0)
        ret.push_back(i);
    bool disjoint = true;
    vector<int> cnt(M, 0);
    for (auto x : {c0.first, c0.second, c1.first, c1.second})
        for (int i : x)
        {
            cnt[i]++;
            if (cnt[i] == 2)
                disjoint = false;
        }
    set<int>S1, S2;
    for (int i : c0.second)
        S1.insert(i);
    for (int i : c1.second)
        S2.insert(i);
    bool gal1 = S1 == S2; if (disjoint) {
        for (int i : c0.first)
            ret.push_back(i);
        for (int i : c0.second)
            ret.push_back(i);
        reverse(c0.first.begin(), c0.first.end());
        for (int i : c0.first)
            ret.push_back(i);
        for (int i : c1.first)
            ret.push_back(i);
        for (int i : c1.second)
            ret.push_back(i);
        reverse(c1.first.begin(), c1.first.end());
        for (int i : c1.first)
            ret.push_back(i);

        reverse(c0.second.begin(), c0.second.end());
        reverse(c1.second.begin(), c1.second.end());


        for (int i : c0.first)
            ret.push_back(i);
        for (int i : c0.second)
            ret.push_back(i);
        reverse(c0.first.begin(), c0.first.end());
        for (int i : c0.first)
            ret.push_back(i);
        for (int i : c1.first)
            ret.push_back(i);
        for (int i : c1.second)
            ret.push_back(i);
        reverse(c1.first.begin(), c1.first.end());
        for (int i : c1.first)
            ret.push_back(i);
    }
    else if (gal1)
    {
        for (int i : c0.first)
            ret.push_back(i);
        for (int i : c0.second)
            ret.push_back(i);
        reverse(c0.first.begin(), c0.first.end());
        for (int i : c0.first)
            ret.push_back(i);
        for (int i : c1.first)
            ret.push_back(i);
        for (int i : c1.second)
            ret.push_back(i);
        reverse(c1.first.begin(), c1.first.end());
        for (int i : c1.first)
            ret.push_back(i);
    }
    else
    {
        vector<int>a = c0.second;
        vector<int>b = c1.second;
        vector<int>c;
        while (a.size() > 0 && a.back() == b.back())
        {
            c.push_back(a.back());
            a.pop_back();
            b.pop_back();
        }
        reverse(c.begin(), c.end());
        for (int i : a)
            ret.push_back(i);
        for (int i : c)
            ret.push_back(i);
        for (int i : b)
            ret.push_back(i);
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());
        reverse(c.begin(), c.end());
        for (int i : a)
            ret.push_back(i);
        for (int i : c)
            ret.push_back(i);
        for (int i : b)
            ret.push_back(i);
    }
    reverse(ans0.begin(), ans0.end());
    for (int i : ans0)
        ret.push_back(i);
    return ret;
}

• Subtask 1: 5 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 15.749999999999998 / 45