Is Toggle Light Bulbs easy or hard?

Toggle Light Bulbs is generally considered an easy problem. The key observation is that toggling the same bulb twice cancels out, so only bulbs toggled an odd number of times remain on. Once that insight is clear, a hash set simulation solves it efficiently.

Toggle Light Bulbs Python/Java solution

The typical implementation uses a set in Python or a HashSet in Java. For each bulb index in the toggle list, check membership and flip the state by inserting or removing it. This produces an O(n) solution with simple and readable code.

How to solve Toggle Light Bulbs in O(n)?

Use a hash set to track bulbs that are currently on. Iterate through the toggle list and flip membership in the set: add the bulb if it is not present, remove it if it already exists. After processing all operations, the remaining elements in the set represent bulbs toggled an odd number of times.

What is the best approach for Toggle Light Bulbs?

The hash set simulation approach is the most efficient. Iterate through each toggle operation and add the bulb to a set if it is off, or remove it if it is already on. This directly models the toggle behavior and runs in O(n) time with O(n) space.

Is Toggle Light Bulbs asked at Google/Amazon/Meta?

Array and hash-table simulation problems like Toggle Light Bulbs appear frequently in interviews at companies such as Amazon, Google, and Meta. The focus is usually on recognizing patterns like parity (odd vs even operations) and using constant-time hash lookups.

What data structure is used in Toggle Light Bulbs?

A hash set or hash map is the most common data structure. The set tracks which bulbs are currently on, while a map can count how many times each bulb was toggled. Arrays may also be used if the bulb range is small and known in advance.

What is the time complexity of Toggle Light Bulbs?

The optimal solution runs in O(n) time where n is the number of toggle operations. Each operation performs a constant-time hash lookup or removal. If the final list of bulbs needs to be sorted, the complexity becomes O(n log n).

Description Hints 1 Solution Video 2:28

3842. Toggle Light Bulbs

Easy71.2% acceptance1 company

You are given an array bulbs of integers between 1 and 100.

There are 100 light bulbs numbered from 1 to 100. All of them are switched off initially.

For each element bulbs[i] in the array bulbs:

If the bulbs[i]^th light bulb is currently off, switch it on.
Otherwise, switch it off.

Return the list of integers denoting the light bulbs that are on in the end, sorted in ascending order. If no bulb is on, return an empty list.

Example 1:

Input: bulbs = [10,30,20,10]

Output: [20,30]

Explanation:

The bulbs[0] = 10^th light bulb is currently off. We switch it on.
The bulbs[1] = 30^th light bulb is currently off. We switch it on.
The bulbs[2] = 20^th light bulb is currently off. We switch it on.
The bulbs[3] = 10^th light bulb is currently on. We switch it off.
In the end, the 20^th and the 30^th light bulbs are on.

Example 2:

Input: bulbs = [100,100]

Output: []

Explanation:

The bulbs[0] = 100^th light bulb is currently off. We switch it on.
The bulbs[1] = 100^th light bulb is currently on. We switch it off.
In the end, no light bulb is on.

Constraints:

1 <= bulbs.length <= 100
1 <= bulbs[i] <= 100

Asked at 1 company

Juspay

Topics

Hints open one at a time

Hint 1

Simulate as described

2:28

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

LanguageLoading editor…

1class Solution:
2    def toggleLightBulbs(self, bulbs: list[int]) -> list[int]:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[10,30,20,10]

Input

[100,100]

Your code is saved on this device.Solution