Submission #854207

#	Time	Username	Problem	Language	Result	Execution time	Memory
854207		boris_mihov	Longest Trip (IOI23_longesttrip)	C++17	100 / 100	10 ms	1128 KiB

longesttrip

#include "longesttrip.h"
#include <algorithm>
#include <iostream>
#include <numeric>
#include <cassert>
#include <random>
#include <vector>

typedef long long llong;
const int MAXN = 256 + 10;
const llong INF = 1e18;
const int INTINF = 1e9;

int n;
std::mt19937 rng(420);
std::vector <int> perm;

std::vector <int> convert(const std::vector <int> &v)
{
    std::vector <int> res;
    for (const int &i : v) res.push_back(perm[i]);
    return res;
}

bool areConnected(std::vector <int> a, std::vector <int> b)
{
    std::vector <int> A, B;
    for (const int &i : a) A.push_back(perm[i]);
    for (const int &i : b) B.push_back(perm[i]);
    return are_connected(A, B);
}

bool areConnected(int a, int b)
{
    std::vector <int> A, B;
    A.push_back(a);
    B.push_back(b);
    return areConnected(A, B);
}

std::vector <int> longest_trip(int N, int D)
{
    n = N;
    std::vector <int> a, b;
    perm.resize(n);
    std::iota(perm.begin(), perm.end(), 0);
    std::shuffle(perm.begin(), perm.end(), rng);
    a.push_back(0);
    b.push_back(1);

    for (int i = 2 ; i < n ; i += 2)
    {
        assert(a.size() && b.size());
        if (i == n - 1)
        {
            if (areConnected(a.back(), i))
            {
                a.push_back(i);
            } else if (areConnected(b.back(), i))
            {
                b.push_back(i);
            } else
            {
                std::reverse(b.begin(), b.end());
                for (const int &u : b)
                {
                    a.push_back(u);
                }

                b.clear();
                b.push_back(i);
            }

            break;
        }   

        if (areConnected(i, i + 1))
        {
            if (areConnected(a.back(), i))
            {
                a.push_back(i);
                a.push_back(i + 1);
                continue;
            }

            if (areConnected(b.back(), i))
            {
                b.push_back(i);
                b.push_back(i + 1);
                continue;
            }

            std::reverse(b.begin(), b.end());
            for (const int &u : b)
            {
                a.push_back(u);
            }

            b.clear();
            b.push_back(i);
            b.push_back(i + 1);
            continue;
        }

        int edgeA = i;
        int edgeB = i;
        if (!areConnected(a.back(), i))
        {
            edgeA = i + 1;
        }

        if (!areConnected(b.back(), i))
        {
            edgeB = i + 1;
        }

        if (edgeA != edgeB)
        {
            a.push_back(edgeA);
            b.push_back(edgeB);
            continue;
        }

        a.push_back(edgeA);
        std::reverse(b.begin(), b.end());
        for (const int &u : b)
        {
            a.push_back(u);
        }

        b.clear();
        b.push_back(edgeB ^ 1);
    }

    if (a.size() < b.size())
    {
        std::swap(a, b);
    }

    if (b.empty())
    {
        return convert(a);
    }

    if (!areConnected(a, b))
    {
        return convert(a);
    }

    if (areConnected({a[0]}, {b[0]}))
    {
        std::reverse(a.begin(), a.end());
        for (int i = 0 ; i < b.size() ; ++i)
        {
            a.push_back(b[i]);
        }

        return convert(a);
    }

    if (b.size() > 1 && areConnected({a[0]}, {b.back()}))
    {
        std::reverse(b.begin(), b.end());
        std::reverse(a.begin(), a.end());
        for (int i = 0 ; i < b.size() ; ++i)
        {
            a.push_back(b[i]);
        }

        return convert(a);
    }

    if (areConnected({b[0]}, {a.back()}))
    {
        for (int i = 0 ; i < b.size() ; ++i)
        {
            a.push_back(b[i]);
        }

        return convert(a);
    }

    int aPos, bPos;
    int l = -1, r = a.size() - 1, mid;
    while (l < r - 1)
    {
        mid = (l + r) / 2;
        std::vector <int> prefix(a.begin(), a.begin() + mid + 1);
        if (!areConnected(prefix, b)) l = mid;
        else r = mid; 
    }

    aPos = r;
    std::vector <int> prefixA(a.begin(), a.begin() + aPos + 1);
    l = -1; r = b.size() - 1;
    while (l < r - 1)
    {
        mid = (l + r) / 2;
        std::vector <int> prefixB(b.begin(), b.begin() + mid + 1);
        if (!areConnected(prefixA, prefixB)) l = mid;
        else r = mid;
    }

    bPos = r;
    for (int i = 0 ; i < aPos ; ++i)
    {
        a.push_back(a[0]);
        a.erase(a.begin());
    }

    for (int i = 0 ; i < bPos ; ++i)
    {
        b.push_back(b[0]);
        b.erase(b.begin());
    }

    std::reverse(a.begin(), a.end());
    for (int i = 0 ; i < b.size() ; ++i)
    {
        a.push_back(b[i]);
    }


    return convert(a);
}

Compilation message (stderr)

longesttrip.cpp: In function 'std::vector<int> longest_trip(int, int)':
longesttrip.cpp:153:28: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  153 |         for (int i = 0 ; i < b.size() ; ++i)
      |                          ~~^~~~~~~~~~
longesttrip.cpp:165:28: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  165 |         for (int i = 0 ; i < b.size() ; ++i)
      |                          ~~^~~~~~~~~~
longesttrip.cpp:175:28: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  175 |         for (int i = 0 ; i < b.size() ; ++i)
      |                          ~~^~~~~~~~~~
longesttrip.cpp:218:24: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  218 |     for (int i = 0 ; i < b.size() ; ++i)
      |                      ~~^~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 25 / 25
• Subtask 4: 60 / 60