LeetCode 672: Bulb Switcher II | CSharp Solution | Math and Pattern Recognition

Master LeetCode 672 Bulb Switcher II, a Medium problem that trips up many candidates who try to simulate it. We cut through the complexity using math and pattern recognition to arrive at an elegant constant-time solution.

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🎯 Discover why only the first 3 bulbs determine all possible outcomes, making brute-force simulation completely unnecessary
🧠 Learn how to spot symmetry and periodicity in toggle problems so you can reason about state without iterating
💻 Walk through a clean, minimal CSharp implementation that handles all edge cases in a few lines
📊 Understand why this reduces to O(1) time and O(1) space once you see the pattern
⚡ Avoid the classic mistake of simulating all n bulbs and all presses when only a 2x3 truth table is needed

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Table of Contents:

00:00 - Understanding problem statement
00:43 - Using backtracking
01:52 - Big O Notation calculated
04:22 - Big O Notation calculated
05:29 - Solution analysis - runtime + memory
05:35 - Conclusion

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⏱️ Time Complexity : O(1)
💾 Space Complexity : O(1)
📌 Difficulty : Medium
🔧 Technique : Math and Pattern Recognition

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1. LeetCode 319 – Bulb Switcher (Medium)
2. LeetCode 292 – Nim Game (Easy)
3. LeetCode 810 – Chalkboard XOR Game (Hard)
4. LeetCode 877 – Stone Game (Medium)

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🔗 LeetCode Problem : https://leetcode.com/problems/bulb-switcher-ii/

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