Submission #706645

#	Time	Username	Problem	Language	Result	Execution time	Memory
706645		danikoynov	Thousands Islands (IOI22_islands)	C++17	100 / 100	167 ms	29964 KiB

islands

#include "islands.h"

#include <variant>
#include <vector>
#include <queue>
#include <iostream>
using namespace std;

const int maxn = 1e5 + 10;
int seen[maxn], in_deg[maxn], out_deg[maxn];
int n, m;
vector < int > links[maxn], rev_links[maxn];
vector < pair < int, int > > graph[maxn];
vector < int > path[3], cycle[3];

int dfs(int node, int id, int root)
{
    if (seen[node] != 0)
        return node;
    ///cout << node << " : " << id << " : " << root << endl;
    seen[node] = 1;
    for (pair < int, int > dest : graph[node])
    {
        if (seen[dest.first] >= 0)
        {
            path[id].push_back(dest.second);
            int up = dfs(dest.first, id, root);
            if (id == 0)
            {
                if (up >= 0)
                {
                    path[id].pop_back();
                    cycle[id].push_back(dest.second);
                    seen[node] = 2;
                }
                else
                    seen[node] = 0;
                if (node != root)
                {
                    if (up == node)
                        return - 1;
                    else
                        return up;
                }
            }
            if (up >= 0 && seen[up] == 1)
            {
                path[id].pop_back();
                cycle[id].push_back(dest.second);
                if (node != root)
                {
                    if (up == node)
                        return -1;
                    else
                        return up;
                }
            }

            if (node != root || id == 1)
                return up;

            id ++;
        }
    }
    return -1;
}

int clear_useless()
{
    queue < int > q;
    for (int i = 0; i < n; i ++)
    {
        if (!out_deg[i])
            q.push(i);
    }

    int start = 0;
    while(!q.empty() || out_deg[start] <= 1)
    {
        if (!q.empty())
        {
            int node = q.front();
            q.pop();
            seen[node] = -1;
            for (int dest : rev_links[node])
            {
                out_deg[dest] --;
                if (out_deg[dest] == 0)
                    q.push(dest);
            }
        }
        while(out_deg[start] <= 1)
        {
            seen[start] = -1;
            out_deg[start] = 0;
            for (int dest : rev_links[start])
            {
                out_deg[dest] --;
                if (out_deg[dest] == 0)
                    q.push(dest);
            }

            pair < int, int > nxt = make_pair(-1, 0);
            for (pair < int, int > cur : graph[start])
            {
                if (seen[cur.first] != -1)
                {
                    nxt = cur;
                    break;
                }
            }

            if (nxt.first == -1)
                return -1;
            start = nxt.first;
            path[2].push_back(nxt.second);
        }
    }

    return start;
}

void append_to_end(vector < int > &base, vector < int > &to_add, int type)
{
    if (type == 0)
    {
        for (int i = 0; i < to_add.size(); i ++)
            base.push_back(to_add[i]);
    }
    else
    {
        for (int i = (int)(to_add.size()) - 1; i >= 0; i --)
            base.push_back(to_add[i]);
    }
}

std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V)
{
    n = N;
    m = M;
    for (int i = 0; i < M; i ++)
    {
        links[U[i]].push_back(V[i]);
        rev_links[V[i]].push_back(U[i]);
        in_deg[V[i]] ++;
        out_deg[U[i]] ++;

        graph[U[i]].push_back({V[i], i});
    }

    int root = clear_useless();
    if (root < 0)
        return false;

    dfs(root, 0, root);
       /** for (int i = 0; i < cycle[1].size(); i  ++)
            cout << cycle[1][i] << " ";
        cout << endl;
        exit(0);*/
    vector < int > ans;
    append_to_end(ans, path[2], 0);
    append_to_end(ans, path[0], 0);
    append_to_end(ans, cycle[0], 1);
    append_to_end(ans, path[0], 1);
    append_to_end(ans, path[1], 0);

    if (cycle[1].empty())
    {
        int ver = V[path[1].back()];
        int idx = 0;
        while(V[cycle[0][idx]] != ver)
            idx ++;
            ///cout << "here " << U[cycle[0][idx]] << " " << V[]
        for (int i = idx; i < cycle[0].size(); i ++)
        ans.push_back(cycle[0][i]);
        for (int i = 0; i < idx; i ++)
            ans.push_back(cycle[0][i]);
    }
    else
        append_to_end(ans, cycle[1], 1);

    append_to_end(ans, path[1], 1);
    if (!cycle[1].empty())
    {
        append_to_end(ans, path[0], 0);
        append_to_end(ans, cycle[0], 0);
        append_to_end(ans, path[0], 1);
        append_to_end(ans, path[1], 0);
        append_to_end(ans, cycle[1], 0);
        append_to_end(ans, path[1], 1);
    }
    append_to_end(ans, path[2], 1);
    return ans;
}

Compilation message (stderr)

islands.cpp: In function 'void append_to_end(std::vector<int>&, std::vector<int>&, int)':
islands.cpp:127:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  127 |         for (int i = 0; i < to_add.size(); i ++)
      |                         ~~^~~~~~~~~~~~~~~
islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:174:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  174 |         for (int i = idx; i < cycle[0].size(); i ++)
      |                           ~~^~~~~~~~~~~~~~~~~

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