Submission #633220

#	Time	Username	Problem	Language	Result	Execution time	Memory
633220		tutis	Thousands Islands (IOI22_islands)	C++17	100 / 100	225 ms	44604 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];
    vector<int>adj_[N];
    for (int i = 0; i < M; i++)
        if (e[U[i]] && e[V[i]])
            adj[U[i]].push_back(i);
    for (int i = 0; i < N; i++)
        if (i != s)
            while (adj[i].size() > 1)
                adj[i].pop_back();
    while (adj[s].size() > 2)
        adj[s].pop_back();
    for (int i = 0; i < N; i++)
        for (int e : adj[i])
        {
            adj_[V[e]].push_back(e);
        }
    vector<int>ret = ans0;
    int ss = 0;
    vector<bool> state(M, false);
    bool fnd = false;
    function<void(int, int)> dfs = [&](int i, int e)->void
    {
        if (i == s && e != -1 && ss == 0)
        {
            fnd = true;
            return;
        }
        for (int ee : adj[i])
        {
            int j = V[ee];
            if (e == ee || state[ee] == true)
                continue;
            state[ee] = true;
            ret.push_back(ee);
            ss++;
            dfs(j, ee);
            ss--;
            if (fnd)
                return;
            ret.pop_back();
            state[ee] = false;
        }
        for (int ee : adj_[i])
        {
            int j = U[ee];
            if (e == ee || state[ee] == false)
                continue;
            state[ee] = false;
            ss--;
            ret.push_back(ee);
            dfs(j, ee);
            if (fnd)
                return;
            ss++;
            ret.pop_back();
            state[ee] = true;
        }
    };
    dfs(s, -1);
    reverse(ans0.begin(), ans0.end());
    for (int i : ans0)
        ret.push_back(i);
    return ret;
}

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