DSA Basics: Complexity Analysis and Recursion

Before any specific data structure makes sense, two questions have to become second nature: how does the work grow as the input grows, and how much memory does that cost. Complexity analysis is the vocabulary interviewers use to ask about trade-offs, and Big-O is how the answer gets written down.

These lessons build that vocabulary visually. Rather than presenting O(n log n) as a formula to remember, the visualizers plot operation counts as the input grows, so the shape of each complexity class is something you have watched rather than memorised. Recursion is covered here too, because the call stack is far easier to reason about once you have seen one drawn.