🔥 LeetCode 137 – Single Number II | C++ Solution

You solved Single Number with XOR. Now the rules changed. Every element appears three times except one. XOR won't save you here. You need to think at the bit level - properly this time. In this video I break down *Single Number II* completely. We start with the brute-force, understand why the XOR trick from part one doesn't work here, and then build up the *bit counting approach* that solves it in O(n) time with no extra space. *Problem:* Every element in the array appears exactly three times except one element which appears only once. Find that element. O(n) time and O(1) space required. Same problem. Different multiplier. Completely different thinking. *What's covered:* - *Brute-force approach* using sorting - where it starts - Why *XOR alone fails* when elements repeat three times - *Bit counting technique* explained from scratch - How counting bits modulo 3 isolates the unique number - *O(n) time, O(1) space* solution with clear dry run - Why this problem is a favourite in *advanced DSA interviews* This is where bit manipulation stops being a trick and starts being a real tool. If you understood Single Number, this one will take your thinking one level deeper. *Try it yourself:* 🔗 https://leetcode.com/problems/single-number-ii/ - - - *Connect with me:* 🌐 Portfolio → https://kamleshchandela-portfolio.netlify.app/ 💼 LinkedIn → https://www.linkedin.com/in/kamlesh-chandela 🐙 GitHub → https://github.com/KamleshChandela 📊 LeetCode → https://leetcode.com/u/KamleshChandela/ 🐦 Twitter → https://x.com/Kamlesh__cg 📧 Email → [email protected] - - - #LeetCode #LeetCode137 #SingleNumberII #BitManipulation #DSA #CPlusPlus #CodingInterview #DataStructures #Algorithms #InterviewPrep #LearnCoding #CodingGita #KamleshChandela #ProblemSolving #CodeWithKamlesh