Submission #839948

#	Time	Username	Problem	Language	Result	Execution time	Memory
839948		emeraldblock	Longest Trip (IOI23_longesttrip)	C++17	85 / 100	21 ms	336 KiB

longesttrip

#include <bits/stdc++.h>
#include <random>
#include "longesttrip.h"

using namespace std;

vector<int> pi,ip;
bool check(vector<int> a, vector<int> b) {
    for (auto& x : a) x = pi[x];
    for (auto& x : b) x = pi[x];
    return are_connected(a,b);
}

vector<int> isline(vector<int> a) {
    for (auto& x : a) x = pi[x];
#ifdef LOCAL
    for (int i = 1; i < a.size(); ++i) {
        assert(are_connected({a[i-1]}, {a[i]}));
    }
#endif
    return a;
}

mt19937 mt(123532);

std::vector<int> longest_trip(int N, int D)
{
    pi.resize(N);
    iota(pi.begin(),pi.end(),0);
    shuffle(pi.begin(),pi.end(),mt);
    vector<int> s1({0}),s2({1});
    for (int i = 2; i < N; ++i) {
        if (check({s1.back()}, {i})) {
            s1.push_back(i);
        } else if (check({s2.back()}, {i})) {
            s2.push_back(i);
        } else {
            while (!s2.empty()) {
                s1.push_back(s2.back());
                s2.pop_back();
            }
            s2.push_back(i);
        }
    }
    // for (auto x : s1) cerr << x << " ";
    // cerr << "\n";
    // for (auto x : s2) cerr << x << " ";
    // cerr << "\n";
    if (!check(s1, s2)) {
        return isline(s1.size() >= s2.size() ? s1 : s2);
    }
    if (check(s1,{s2.front()})) {
            reverse(s2.begin(),s2.end());
    } else {
        int lo = 0, hi = s2.size();
        while (hi-lo>1) {
            int mid = (lo+hi)/2;
            vector<int> v;
            for (int i = mid; i < hi; ++i) {
                v.push_back(s2[i]);
            }
            if (!check(s1, v)) {
                hi = mid;
            } else {
                lo = mid;
            }
        }
        rotate(s2.begin(),s2.begin()+hi,s2.end());
    }
    if (check({s1.front()},{s2.back()})) {
        reverse(s1.begin(),s1.end());
    } else {
        int lo = 0, hi = s1.size();
        while (hi-lo>1) {
            int mid = (lo+hi)/2;
            vector<int> v;
            for (int i = mid; i < hi; ++i) {
                v.push_back(s1[i]);
            }
            if (!check(v, {s2.back()})) {
                hi = mid;
            } else {
                lo = mid;
            }
        }
        rotate(s1.begin(),s1.begin()+hi,s1.end());
    }
    // for (auto x : s1) cerr << x << " ";
    // cerr << "\n";
    // for (auto x : s2) cerr << x << " ";
    // cerr << "\n";
    while (!s2.empty()) {
        s1.push_back(s2.back());
        s2.pop_back();
    }
    return isline(s1);
}

• Subtask 0: 0 / 0
• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 25 / 25
• Subtask 4: 45 / 60