Submission #836418

#	Time	Username	Problem	Language	Result	Execution time	Memory
836418		SamAnd	Thousands Islands (IOI22_islands)	C++17	55 / 100	38 ms	6136 KiB

islands

#include "islands.h"
#include <variant>
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define m_p make_pair
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
typedef long long ll;
const int N = 1003, M = 200005;

vector<pair<int, int> > g[N];
vector<int> ans;

int c[N];
int pi[N];
int p[N];
bool dfs(int x)
{
    c[x] = 1;
    for (int i = 0; i < g[x].size(); ++i)
    {
        int h = g[x][i].fi;
        int hi = g[x][i].se;
        if (c[h] == 1)
        {
            vector<int> s;
            int y = h;
            while (y)
            {
                s.push_back(pi[y]);
                y = p[y];
            }
            reverse(all(s));

            vector<int> v;
            y = x;
            while (y != h)
            {
                v.push_back(pi[y]);
                y = p[y];
            }
            reverse(all(v));
            v.push_back(hi);

            for (int i = 0; i < sz(s); ++i)
                ans.push_back(s[i]);
            for (int i = 0; i < sz(v); ++i)
                ans.push_back(v[i]);
            for (int i = 0; i < sz(v); ++i)
                ans.push_back((v[i] ^ 1));
            for (int i = sz(v) - 1; i >= 0; --i)
                ans.push_back(v[i]);
            for (int i = sz(v) - 1; i >= 0; --i)
                ans.push_back((v[i] ^ 1));
            for (int i = sz(s) - 1; i >= 0; --i)
                ans.push_back(s[i]);
            return true;
        }
        else if (!c[h])
        {
            p[h] = x;
            pi[h] = hi;
            if (dfs(h))
                return true;
        }
    }
    c[x] = 2;
    return false;
}

std::variant<bool, std::vector<int> > find_journey(int N, int M, std::vector<int> U, std::vector<int> V)
{
    for (int i = 0; i < M; ++i)
    {
        g[U[i]].push_back(m_p(V[i], i));
    }
    if (N == 2)
    {
        if (sz(g[0]) >= 2 && sz(g[1]) >= 1)
        {
            ans.push_back(g[0][0].se);
            ans.push_back(g[1][0].se);
            ans.push_back(g[0][1].se);
            ans.push_back(g[0][0].se);
            ans.push_back(g[1][0].se);
            ans.push_back(g[0][1].se);
            return ans;
        }
        return false;
    }

    bool z = true;
    if (M % 2 == 1)
    {
        z = false;
    }
    else
    {
        for (int i = 0; i < M; i += 2)
        {
            if (m_p(U[i], V[i]) != m_p(V[i + 1], U[i + 1]))
            {
                z = false;
                break;
            }
        }
    }

    if (z)
    {
        int x = 0;
        while (1)
        {
            vector<pair<int, int> > v;
            for (int i = 0; i < g[x].size(); ++i)
            {
                int h = g[x][i].fi;
                int hi = g[x][i].se;
                if (!ans.empty() && ans.back() / 2 == hi / 2)
                    continue;
                v.push_back(m_p(h, hi));
            }
            if (v.empty())
                return false;
            if (sz(v) == 1)
            {
                ans.push_back(v[0].se);
                x = v[0].fi;
                continue;
            }
            vector<int> yans = ans;
            ans.push_back(v[0].se);
            ans.push_back((v[0].se ^ 1));
            ans.push_back(v[1].se);
            ans.push_back((v[1].se ^ 1));
            ans.push_back((v[0].se ^ 1));
            ans.push_back(v[0].se);
            ans.push_back((v[1].se ^ 1));
            ans.push_back(v[1].se);
            for (int i = sz(yans) - 1; i >= 0; --i)
                ans.push_back(yans[i]);
            return ans;
        }
        assert(false);
    }

    z = true;
    if (M % 2 == 1)
    {
        z = false;
    }
    else
    {
        for (int i = 0; i < M; i += 2)
        {
            if (m_p(U[i], V[i]) != m_p(U[i + 1], V[i + 1]))
            {
                z = false;
                break;
            }
        }
    }

    if (z)
    {
        if (!dfs(0))
            return false;
        return ans;
    }
    else
    {
        int k0, k1, k2, k3;
        for (int i = 0; i < g[0].size(); ++i)
        {
            int h = g[0][i].fi;
            int hi = g[0][i].se;
            if (h == 1)
            {
                k0 = hi;
            }
            if (h == 2)
            {
                k1 = hi;
            }
        }
        for (int i = 0; i < g[1].size(); ++i)
        {
            int h = g[1][i].fi;
            int hi = g[1][i].se;
            if (h == 0)
            {
                k2 = hi;
            }
        }
        for (int i = 0; i < g[2].size(); ++i)
        {
            int h = g[2][i].fi;
            int hi = g[2][i].se;
            if (h == 0)
            {
                k3 = hi;
            }
        }
        ans.push_back(k0);
        ans.push_back(k2);
        ans.push_back(k1);
        ans.push_back(k3);
        ans.push_back(k2);
        ans.push_back(k0);
        ans.push_back(k3);
        ans.push_back(k1);
        return ans;
    }
}

/*int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> u, v;
    for (int i = 0; i < m; ++i)
    {
        int x, y;
        cin >> x >> y;
        u.push_back(x);
        v.push_back(y);
    }
    cout << find_journey(n, m, u, v) << "\n";
    return 0;
}*/

/*
5 6
0 1
1 0
1 3
3 1
0 4
4 0

3 6
0 1
1 0
1 2
2 1
2 0
0 2
*/

Compilation message (stderr)

islands.cpp: In function 'bool dfs(int)':
islands.cpp:22:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |     for (int i = 0; i < g[x].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:117:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  117 |             for (int i = 0; i < g[x].size(); ++i)
      |                             ~~^~~~~~~~~~~~~
islands.cpp:175:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  175 |         for (int i = 0; i < g[0].size(); ++i)
      |                         ~~^~~~~~~~~~~~~
islands.cpp:188:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  188 |         for (int i = 0; i < g[1].size(); ++i)
      |                         ~~^~~~~~~~~~~~~
islands.cpp:197:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  197 |         for (int i = 0; i < g[2].size(); ++i)
      |                         ~~^~~~~~~~~~~~~

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