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. --- 🎯 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 --- 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 --- ⏱️ Time Complexity : O(1) 💾 Space Complexity : O(1) 📌 Difficulty : Medium 🔧 Technique : Math and Pattern Recognition --- 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) --- 🔗 LeetCode Problem : https://leetcode.com/problems/bulb-switcher-ii/ --- If this explanation clicked for you, hit the like button and subscribe so you never miss a solution. Drop your questions or alternative approaches in the comments below, every question helps the whole community level up. --- #leetcode #csharp #codinginterview #dsa #leetcode672 #bulbswitcher #mathproblem #patternrecognition #dotnet #mediumleetcode #interviewprep #competitiveprogramming #algorithmsanddatastructures #techinteview #leetcodesolution