Submission #633187

#	Time	Username	Problem	Language	Result	Execution time	Memory
633187		tutis	Thousands Islands (IOI22_islands)	C++17	55 / 100	50 ms	11652 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;
            if (!c.empty())
                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)
            {
                vector<int>a = xx;
                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]);
                reverse(a.begin(), a.end());
                for (int i : a)
                    c.push_back(i);
            }
            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;
    }
    {
        vector<pair<int, int>>adj[N];
        for (int i = 0; i + 1 < M; i += 2)
            if (U[i + 1] == U[i] && V[i] == V[i + 1])
                adj[U[i]].push_back({V[i], i});
        vector<bool> vis(N, false);
        vector<bool> st(N, false);
        vector<int>c;
        vector<int>xx;
        vector<int> D(N);
        function<void(int, int)>dfs = [&](int i, int d)->void
        {
            if (vis[i])
                return;
            if (!c.empty())
                return;
            D[i] = d;
            vis[i] = true;
            for (pair<int, int> jj : adj[i])
            {
                int j = jj.first;
                if (st[j] == true)
                {
                    xx.push_back(jj.second);
                    vector<int>a, b;
                    for (int i = 0; i < D[j]; i++)
                        a.push_back(xx[i]);
                    for (int i = D[j]; i < (int)xx.size(); i++)
                        b.push_back(xx[i]);
                    for (int i : a)
                        c.push_back(i);
                    for (int i : b)
                        c.push_back(i);
                    for (int i : b)
                        c.push_back(i ^ 1);
                    reverse(b.begin(), b.end());
                    reverse(a.begin(), a.end());
                    for (int i : b)
                        c.push_back(i);
                    for (int i : b)
                        c.push_back(i ^ 1);
                    for (int i : a)
                        c.push_back(i);
                    return;
                }
            }
            for (pair<int, int> jj : adj[i])
            {
                int j = jj.first;
                if (vis[j] == false)
                {
                    xx.push_back(jj.second);
                    st[j] = true;
                    dfs(j, d + 1);
                    st[j] = false;
                    xx.pop_back();
                    if (!c.empty())
                        return;
                }
            }
        };
        st[0] = true;
        dfs(0, 0);
        if (!c.empty())
            return c;
    }
    {
        vector<pair<int, int>>adj[N];
        for (int i = 0; i < M; i++)
            adj[U[i]].push_back({V[i], i});
        vector<bool> vis(N, false);
        vector<bool> st(M, false);
        vector<bool> stV(N, false);
        vector<int> cid(N, -1);
        vector<int>c;
        vector<int>xx;
        vector<int> D(N);
        vector<int> E(N);
        function<void(int, int)>dfs = [&](int i, int d)->void
        {
            if (vis[i])
                return;
            if (!c.empty())
                return;
            D[i] = d;
            vis[i] = true;
            for (pair<int, int> jj : adj[i])
            {
                int j = jj.first;
                if (vis[j] == false)
                {
                    xx.push_back(jj.second);
                    st[jj.second] = true;
                    stV[jj.first] = true;
                    E[i] = jj.second;
                    dfs(j, d + 1);
                    if (cid[j] != -1)
                    {
                        if (U[cid[j]] != j)
                        {
                            if (cid[i] == -1)
                                cid[i] = cid[j];
                            else if (D[U[cid[i]]] < D[U[cid[j]]])
                                cid[i] = cid[j];
                        }
                    }
                    st[jj.second] = false;
                    stV[jj.first] = false;
                    xx.pop_back();
                    if (!c.empty())
                        return;
                }
                else
                {
                    if (stV[j])
                    {
                        int e = E[j];
                        if (cid[i] == -1)
                            cid[i] = e;
                        else if (D[U[cid[i]]] < D[j])
                            cid[i] = e;
                    }
                    if (cid[j] != -1)
                    {
                        if (!st[cid[j]])
                        {
                            c = {1, 2, 0};
                            return;
                        }
                    }
                }
            }
        };
        stV[0] = true;
        dfs(0, 0);
        stV[0] = false;
        if (!c.empty())
            return c;
    }
    return false;
}

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