Design Parking System

Problem

Design a parking system for a lot with three slot sizes: big, medium, and small, with a fixed number of each. Implement ParkingSystem(int big, int medium, int small) and boolean addCar(int carType) where carType is 1 (big), 2 (medium), or 3 (small). Return true if a slot of that size is free (and occupy it), else false.

Constraints

• 0 ≤ big, medium, small ≤ 1000
• carType ∈ {1, 2, 3}
• at most 1000 addCar calls

Approach — Hashing & Counting

This is a Hashing & Counting problem. The idea: store what you've seen in a hash map for O(1) lookups, trading a little space to avoid a nested scan. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(n) space.

Solution code

Python

class ParkingSystem:
    def __init__(self, big, medium, small):
        self.slots = {1: big, 2: medium, 3: small}

    def addCar(self, carType):
        if self.slots[carType] > 0:
            self.slots[carType] -= 1
            return True
        return False

Java

class ParkingSystem {
    private int[] slots;

    public ParkingSystem(int big, int medium, int small) {
        // index 0 unused so carType maps directly to an index
        slots = new int[]{0, big, medium, small};
    }

    public boolean addCar(int carType) {
        if (slots[carType] > 0) {
            slots[carType]--;
            return true;
        }
        return false;
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.