two-pointers

Leetcode considers this question to be easy, but it was a bit more complicated than that at first for me. Let’s try solving it three different ways: Whenever I can, I always try to do BFS. It seems much more natural. BFS - 1st solution func isSymmetricBFS(_ root: TreeNode?) -> Bool { var queue: [TreeNode?] = [] queue.append(root) while !queue.isEmpty { let temp = queue queue.removeAll() // 🔑 to make sure you don't expand on `nil` nodes — otherwise it would be endless for node in temp where node !...

Today I’m going to discuss another fun and common challenge. It’s the Longest Common Subsequence a.k.a. LCS. I’ll first focus on discussing a pain point I went through when I was trying to compare the algorithm I deduced on my own vs a few other algorithms I saw online. Our algorithms seemed very similar. Yet different. It made debugging my code based on other code very difficult. This is a very common problem I face when I doing leetcode....