Submission #1067613

#	Time	Username	Problem	Language	Result	Execution time	Memory
1067613		golf	Longest Trip (IOI23_longesttrip)	C++17	40 / 100	11 ms	600 KiB

longesttrip

#include "longesttrip.h"
#include <bits/stdc++.h>
using namespace std;

vector<int> solve_d3(int N, int D) {
    vector<int> res(N);
    iota(res.begin(), res.end(), 0);
    return res;
}

vector<int> solve_d2(int N, int D) {
    queue<int> stops;
    for (int i = 1; i < N; i++) stops.push(i);

    deque<int> trip = {0};
    while (stops.size() > 1) {
        int next = stops.front(); stops.pop();
        int last = trip.back();
        
        if (are_connected({next}, {last})) {
            trip.push_back(next);
        } else {
            trip.push_back(stops.front()); stops.pop();
            trip.push_back(next);
        }
    }

    if (stops.size() == 1) {
        int next = stops.front();
        int last = trip.back();
        if (are_connected({next}, {last})) {
            trip.push_back(next);
        } else {
            trip.push_front(stops.front()); stops.pop();
        }
    }

    vector<int> res;
    for (int x : trip) res.push_back(x);
    return res;
}


int pop(queue<int> &q) {
    int x = q.front();
    q.pop();
    return x;
}

const bool maybe = true;

vector<int> longest_trip(int N, int D) {
    if (D == 3) return solve_d3(N, D);
    if (D == 2) return solve_d2(N, D);

    queue<int> nodes;
    for (int i = 0; i < N; i++) nodes.push(i);

    vector<int> a, b;
    a.push_back(pop(nodes));

    bool ends_connected = maybe;
    // false = a and b are not connected
    // true  = a and b are maybe connected
    while (!nodes.empty()) {
        if (b.empty()) {
            int n = pop(nodes);
            if (are_connected({a.back()}, {n})) {
                a.push_back(n);
            } else {
                // missed optimization
                // we could cache that a and b are not connected
                b.push_back(n);
                ends_connected = false;
            }
            continue;
        }

        // both a and b are non-empty
        int n = pop(nodes);

        if (are_connected({a.back()}, {n})) {
            a.push_back(n);
            ends_connected = maybe;
        } else if (are_connected({b.back()}, {n})) {
            b.push_back(n);
            ends_connected = false;
        } else {
            // ends of a and b are definitely connected
            while(!b.empty()) {
                a.push_back(b.back());
                b.pop_back();
            }

            assert(b.empty());
            b.push_back(n);
        }
    }

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

    if (ends_connected == maybe && are_connected({a.back()}, {b.back()})) {
        while(!b.empty()) {
            a.push_back(b.back());
            b.pop_back();
        }

        return a;
    }

    if (!are_connected(a, b)) {
        if (a.size() > b.size()) {
            return a;
        } else {
            return b;
        }
    }

    // not finished
    if (a.size() > b.size()) {
        return a;
    } else {
        return b;
    }
}

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