Design Parking System - Practice Coding Problems

Design Parking System - Problem

Design a parking system for a parking lot. The parking lot has three kinds of parking spaces: big, medium, and small, with a fixed number of slots for each size.

Implement the ParkingSystem class:

ParkingSystem(int big, int medium, int small) Initializes object of the ParkingSystem class. The number of slots for each parking space are given as part of the constructor.
bool addCar(int carType) Checks whether there is a parking space of carType for the car that wants to get into the parking lot. carType can be of three kinds: big, medium, or small, which are represented by 1, 2, and 3 respectively. A car can only park in a parking space of its carType. If there is no space available, return false, else park the car in that size space and return true.

Input & Output

Example 1 — Basic Operations

$ Input: operations = ["ParkingSystem", "addCar", "addCar", "addCar", "addCar"], values = [[1,1,0], [1], [2], [3], [1]]

› Output: [null, true, true, false, false]

💡 Note: Initialize parking system with 1 big space, 1 medium space, 0 small spaces. First big car parks successfully, medium car parks successfully, small car fails (no spaces), second big car fails (space occupied).

Example 2 — Multiple Spaces

$ Input: operations = ["ParkingSystem", "addCar", "addCar", "addCar"], values = [[2,2,1], [1], [1], [2]]

› Output: [null, true, true, true]

💡 Note: Initialize with 2 big, 2 medium, 1 small space. Two big cars park successfully, then one medium car parks successfully.

Example 3 — No Available Spaces

$ Input: operations = ["ParkingSystem", "addCar", "addCar"], values = [[0,0,0], [1], [2]]

› Output: [null, false, false]

💡 Note: No spaces of any type available, so all cars are rejected.

Constraints

1 ≤ big, medium, small ≤ 1000
carType is 1, 2, or 3
At most 1000 calls will be made to addCar

Visualization

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Understanding the Visualization

Initialize

Create parking system with specified space counts

Add Car

Check availability and park car if space exists

Track Usage

Update available space count for that type

Key Takeaway

🎯 Key Insight: Only track remaining space counts, not individual slot locations - this achieves O(1) efficiency

Asked in

a Amazon 25 G Google 15 M Microsoft 12

The optimal approach uses simple counters to track available spaces for each car type. Key insight: we only need to know how many spaces remain, not which specific slots are occupied. Time: O(1) per operation, Space: O(1) total.

Common Approaches

Approach	Time	Space	Notes
✓ Counter-Based Tracking	O(1)	O(1)	Use simple counters to track remaining spaces
Array-Based Tracking	O(n)	O(n)	Use arrays to track each individual parking space

Counter-Based Tracking — Algorithm Steps

Initialize counters for big, medium, small spaces
For addCar, check if counter > 0
If yes, decrement counter and return true, else return false

Visualization

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Step-by-Step Walkthrough

Initialize Counters

Store available space counts for each type

Check Availability

Simply check if counter > 0 in O(1) time

Update Counter

Decrement counter if space available

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

typedef struct {
    int big;
    int medium;
    int small;
} ParkingSystem;

ParkingSystem* parkingSystemCreate(int big, int medium, int small) {
    ParkingSystem* ps = (ParkingSystem*)malloc(sizeof(ParkingSystem));
    ps->big = big;
    ps->medium = medium;
    ps->small = small;
    return ps;
}

bool parkingSystemAddCar(ParkingSystem* ps, int carType) {
    if (carType == 1) {
        if (ps->big > 0) {
            ps->big--;
            return true;
        }
    } else if (carType == 2) {
        if (ps->medium > 0) {
            ps->medium--;
            return true;
        }
    } else if (carType == 3) {
        if (ps->small > 0) {
            ps->small--;
            return true;
        }
    }
    return false;
}

int main() {
    ParkingSystem* ps = parkingSystemCreate(1, 1, 0);
    printf("[null,%s,%s,%s]\n", 
           parkingSystemAddCar(ps, 1) ? "true" : "false",
           parkingSystemAddCar(ps, 2) ? "true" : "false",
           parkingSystemAddCar(ps, 3) ? "true" : "false");
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Each addCar operation only checks and decrements a counter

✓ Linear Growth

Space Complexity

O(1)

Only store three integer counters regardless of parking lot size

✓ Linear Space

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Counter-Based Tracking — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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