Submission #1239436

#	Time	Username	Problem	Language	Result	Execution time	Memory
1239436		tapilyoca	Parking (CEOI22_parking)	C++20	20 / 100	282 ms	23640 KiB

Main

/***********************************************
* auth: tapilyoca                              *
* date: 07/13/2025 at 15:50:36                 *
* dots: https://github.com/tapilyoca/dotilyoca * 
***********************************************/

#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9+7;

template<typename T>
using vec = vector<T>;
using ll = int;
using vll = vec<ll>;
using vvll = vec<vll>;
using pll = pair<ll,ll>;
using str = string;
#define pb push_back
#define dbg(x) if(1) cerr << #x << ": " << x << endl;

/***********************************************/

struct ParkingSpot {
    ll topCar, botCar;
    ll sz;

    ParkingSpot(ll x, ll y) {
        if(x == 0) {
            topCar = botCar = sz = 0;
        } 
        else if(y == 0) {
            topCar = x;
            sz = 1;
            botCar = 0;
        } else {
            topCar = y;
            botCar = x;
            sz = 2;
        }
    }

    ParkingSpot() : topCar(0), botCar(0), sz(0) {}

    void push_car(ll c) {
        assert(sz < 2);
        botCar = topCar;
        topCar = c;
        sz++;
    }

    ll pop_top() {
        ll temp = topCar;
        topCar = botCar;
        botCar = 0;
        sz--;
        return temp;
    }

    void print() {
        cerr << topCar << " " << botCar << endl;
    }
};

vec<ParkingSpot> parking;
map<ll,set<ll>> topCarToSpot;
queue<ll> free_colors, almost_free_colors;
vec<pll> output;
queue<ll> empties;

void drive_car(ll from, ll to) {
    // cerr << "Driving " << from << " to " << to << endl;

    if(parking[from].sz == 0) {
        cerr << "WHAT THE HELL ARE YOU DOING" << endl;
        assert(0);
    }

    if(parking[to].sz == 2) {
        cerr << "CANT PUSH CAR HERE, " << to << " FULL" << endl;
        assert(0);
    }

    topCarToSpot[parking[from].topCar].erase(from);
    topCarToSpot[parking[from].topCar].insert(to);

    parking[to].push_car(parking[from].pop_top());

    // update our sets
    if(parking[from].sz == 0) {
        empties.push(from);
    } else {
        ll ccar = parking[from].topCar;
        topCarToSpot[ccar].insert(from);
        if(topCarToSpot[ccar].size() == 2) {
            if(parking[*topCarToSpot[ccar].begin()].sz + parking[*topCarToSpot[ccar].rbegin()].sz < 4) {
                free_colors.push(ccar);
            } else {
                almost_free_colors.push(ccar);
            }
        }
    }

    output.pb({from,to});
}

void drive_car_2(ll from, ll to) {
    // cerr << "Mriving " << from << " " << to << endl;
    parking[to].push_car(parking[from].pop_top());
    output.pb({from,to});
}

void bruh(queue<ll> q) {
    while(!q.empty()) {
        cerr << q.front() << " ";
        q.pop();
    }
}

void solve() {
    ll n, m;
    cin >> n >> m;
    parking.resize(m);

    for(int i = 0; i < m; i++) {
        ll x, y;
        cin >> x >> y;
        parking[i] = {x,y};
    }


    for(int i = 0; i < m; i++) {
        if(parking[i].sz == 0) {
            empties.push(i);
            continue;
        }
        ll car = parking[i].topCar;
        if(car) topCarToSpot[car].insert(i);
        if(topCarToSpot[car].size() == 2) {
            // cerr << car << ": " << *topCarToSpot[car].begin() << " " << *topCarToSpot[car].rbegin() << endl;
            // check if this can be a free move
            if(parking[*topCarToSpot[car].begin()].sz + parking[*topCarToSpot[car].rbegin()].sz < 4) {
                free_colors.push(car);
            } else {
                almost_free_colors.push(car);
            }
        }
    }

    // cerr << "Free colors: ";
    // bruh(free_colors);

    // cerr << "\nAlmost free colors: ";
    // bruh(almost_free_colors);
    // cerr << endl;

    while(!free_colors.empty() or (!almost_free_colors.empty() and !empties.empty())) {
        if(!free_colors.empty()) {
            ll car = free_colors.front();
            free_colors.pop();
                        
            if(parking[*topCarToSpot[car].begin()].sz == 2) {
                drive_car(*topCarToSpot[car].begin(), *topCarToSpot[car].rbegin());
            } else {
                drive_car(*topCarToSpot[car].rbegin(), *topCarToSpot[car].begin());
            }
        }

        if(!almost_free_colors.empty() and !empties.empty()) {
            ll car = almost_free_colors.front();
            almost_free_colors.pop();
            ll empty_spot = empties.front();
            empties.pop();

            parking[empty_spot] = {car, car};
            ll f1 = *topCarToSpot[car].begin(), f2 = *topCarToSpot[car].rbegin();
            parking[f1].pop_top();
            parking[f2].pop_top();

            output.pb({f1, empty_spot});
            output.pb({f2, empty_spot});

            if(parking[f1].sz == 0) empties.push(f1);
            else {
                ll f1c = parking[f1].topCar;
                topCarToSpot[f1c].insert(f1);
                if(topCarToSpot[f1c].size() == 2) {
                    if(parking[*topCarToSpot[f1c].begin()].sz + parking[*topCarToSpot[f1c].rbegin()].sz < 4) {
                        free_colors.push(f1c);
                    } else {
                        almost_free_colors.push(f1c);
                    }
                }
            }
            if(parking[f2].sz == 0) empties.push(f2);
            
            else {
                ll f2c = parking[f2].topCar;
                topCarToSpot[f2c].insert(f2);
                if(topCarToSpot[f2c].size() == 2) {
                    if(parking[*topCarToSpot[f2c].begin()].sz + parking[*topCarToSpot[f2c].rbegin()].sz < 4) {
                        free_colors.push(f2c);
                    } else {
                        almost_free_colors.push(f2c);
                    }
                }
            }
            // drive_car(*topCarToSpot[car].begin(), empty_spot);
            // drive_car(*topCarToSpot[car].rbegin(), empty_spot);
        }
    }

    if(!almost_free_colors.empty() and empties.empty()) {
        cout << -1 << endl;
        return;
    }

    // cerr << "Ok done with that now doing cycles" << endl;
    map<ll,ll> carToTopPosn;
    for(int i = 0; i < m; i++) {
        carToTopPosn[parking[i].topCar] = i;
    }

    for(int i = 0; i < m; i++) {
        if(parking[i].topCar == parking[i].botCar or parking[i].topCar == 0) continue;

        if(empties.empty()) {
            cout << -1 << endl;
            return;
        }

        // fix this cycle
        ll curr = i;
        // dbg(i);
        ll emptySlot = empties.front();
        empties.pop();

        drive_car_2(i,emptySlot);
        
        do {
            ll former = curr;
            curr = carToTopPosn[parking[curr].topCar];
            // cerr << "f/c: " << former << " " << curr << endl;
            if(curr == i) {
                drive_car_2(former,emptySlot);
                empties.push(curr);
                break;
            } else {
                drive_car_2(curr,former);
            }
        } while(curr != i);

        // cerr << "Done with " << i << " heres parking: " << endl;
        // for(int i = 0; i < m; i++) {
        //     cerr << parking[i].botCar << " " << parking[i].topCar << endl;
        // }
    }

    cout << output.size() << endl;
    for(auto[x,y] : output) cout << x+1 << " " << y+1 << endl;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    int t = 1;

    while(t--) {
        solve();
    }

    return 0;
}


/*

0 1 2 3 4 X
1 2 3 4 0 X

0 1 3 3 4 0 0
1 2 2 4 5 5 0

1 0 3 3 4 0 0
1 2 2 4 5 5 0

1 0 0 3 4 0 0
1 2 2 4 5 5 3

1 0 0 3 4 0 0
1 2 2 4 5 5 3

*/

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 25
• Subtask 4: 0 / 15
• Subtask 5: 0 / 25
• Subtask 6: 0 / 15