Leetcode #1603: Design Parking System
In this guide, we solve Leetcode #1603 Design Parking System in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
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.
Quick Facts
- Difficulty: Easy
- Premium: No
- Tags: Design, Counting, Simulation
Intuition
The output depends on how often values appear.
Counting frequencies lets us answer queries in constant time afterward.
Approach
Count occurrences with a map or array, then compute the result from those counts.
This avoids repeated scans of the input.
Steps:
- Count frequencies.
- Use counts to compute result.
- Return the computed value.
Example
Input
["ParkingSystem", "addCar", "addCar", "addCar", "addCar"]
[[1, 1, 0], [1], [2], [3], [1]]
Output
[null, true, true, false, false]
Explanation
ParkingSystem parkingSystem = new ParkingSystem(1, 1, 0);
parkingSystem.addCar(1); // return true because there is 1 available slot for a big car
parkingSystem.addCar(2); // return true because there is 1 available slot for a medium car
parkingSystem.addCar(3); // return false because there is no available slot for a small car
parkingSystem.addCar(1); // return false because there is no available slot for a big car. It is already occupied.
Python Solution
class ParkingSystem:
def __init__(self, big: int, medium: int, small: int):
self.cnt = [0, big, medium, small]
def addCar(self, carType: int) -> bool:
if self.cnt[carType] == 0:
return False
self.cnt[carType] -= 1
return True
# Your ParkingSystem object will be instantiated and called as such:
# obj = ParkingSystem(big, medium, small)
# param_1 = obj.addCar(carType)
Complexity
The time complexity is , and the space complexity is . The space complexity is .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.