Coding Problem : Concatenation of Array in One Loop (JS) | The Modulo Pattern

The modulo wrap pattern, taught through one problem. Same problem as Part 1 (Concatenation of Array), same complexity (O(n) time, O(1) auxiliary), but a single loop using ans[i] = nums[i % n] — and a trick that reuses across array rotations, ring buffers, hash probing, and more. In this Part 2, I walk it end-to-end the way I want a new programmer to see it: refresher → turntable analogy → flow chart → JavaScript line by line → algorithm trace → complexity → two traps every dev still writes → where the pattern shows up next. KEY TAKEAWAYS → Single loop, 2n iterations: ans[i] = nums[i % n] → The modulo wraps reads back to nums[0..n-1] for the second half → Same O(n) / O(1) complexity as Part 1 — cleaner code, better cache locality → Pattern reuses: array rotations, ring buffers, circular queues, hash table probing → JS gotcha: negative modulo preserves sign — use ((i % n) + n) % n when indices can be negative CHAPTERS 0:00 Cold open 0:12 Same problem, different approach 0:30 Refresher + constraints 1:10 Mentor pause 1:30 Turntable analogy 1:55 Flow chart — 4 boxes 2:25 Modulo mini-quiz 2:45 Pseudocode 3:10 JavaScript walkthrough 4:00 Why i % n works 4:35 Trace 5:30 Complexity 6:00 Two traps 6:45 Part 1 vs Part 2 7:20 Recap + outro 📚 Playlist: Coding Problems Decoded — One Pattern at a Time 📌 Topic: Coding Problems — Arrays & Two Pointers #CodingProblems #CodingProblem #Arrays #DSA #JavaScript #Codebrainery