Submission #633112

#	Time	Username	Problem	Language	Result	Execution time	Memory
633112		tutis	Thousands Islands (IOI22_islands)	C++17	17.35 / 100	31 ms	4416 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) {
    if (N == 2)
    {
        vector<int>a;
        vector<int>b;
        for (int i = 0; i < M; i++)
            if (U[i] == 0 && V[i] == 1)
                a.push_back(i);
            else
                b.push_back(i);
        if (a.size() >= 2 && b.size() >= 1)
            return vector<int>({a[0], b[0], a[1], a[0], b[0], a[1]});
        return false;
    }
    {
        int x = -1;
        int y = -1;
        int z = -1;
        int t = -1;
        for (int i = 0; i < M; i++)
            if (U[i] == 0 && V[i] == 1)
                x = i;
            else if (U[i] == 1 && V[i] == 0)
                y = i;
            else if (U[i] == 0 && V[i] == 2)
                z = i;
            else if (U[i] == 2 && V[i] == 0)
                t = i;
        if (min({x, y, z, t}) >= 0)
            return vector<int>({x, y, z, t, y, x, t, z});
    }
    {
        vector<pair<int, int>>adj[N];
        for (int i = 0; i + 1 < M; i += 2)
            if (V[i + 1] == U[i] && V[i] == U[i + 1])
            {
                adj[U[i]].push_back({V[i], i});
                adj[V[i]].push_back({U[i], i + 1});
            }
        vector<bool> vis(N, false);
        vector<int>c;
        vector<int>xx;
        function<void(int)>dfs = [&](int i)->void
        {
            if (vis[i])
                return;
            vis[i] = true;
            vector<int>V;
            for (pair<int, int> jj : adj[i])
            {
                int j = jj.first;
                if (vis[j] == false)
                    V.push_back(jj.second);
            }
            if (V.size() >= 2)
            {
                c = xx;
                c.push_back(V[0]);
                c.push_back(V[0] ^ 1);
                c.push_back(V[1]);
                c.push_back(V[1] ^ 1);
                c.push_back(V[0] ^ 1);
                c.push_back(V[0]);
                c.push_back(V[1] ^ 1);
                c.push_back(V[1]);
            }
            else
                for (pair<int, int> jj : adj[i])
                {
                    int j = jj.first;
                    if (vis[j] == false)
                    {
                        xx.push_back(jj.second);
                        dfs(j);
                        xx.pop_back();
                        if (!c.empty())
                            return;
                    }
                }
        };
        dfs(0);
        if (!c.empty())
            return c;
    }
    return false;
}

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