Print All Root-to-Leaf Tree Paths

MLE / Applied Research Set B opener. Given a binary tree (or general tree, depending on variant), print every root-to-leaf path. Standard recursive DFS — the round uses it as a warm-up before the deployment / latency discussion. Requirements Input: the root of a binary tree (each node has val, left, right). Return a list of all root-to-leaf paths. Each path is the sequence of node values from the root down to a leaf. Edge cases: empty tree returns []; a single-node tree returns [[root.val]]. Examples 1 / \ 2 3 \ 5 Return [[1, 2, 5], [1, 3]] Notes Canonical recursive DFS: carry a running path as a list, append at each recursive call, recurse into left and right, and emit a copy when a leaf is hit. The classic LeetCode 257 Binary Tree Paths shape. Iterative variant uses an explicit stack of (node, path_so_far) tuples — useful if the interviewer asks about deep trees and recursion limits. Common bug: appending the live path reference into the result list instead of a copy. Use result.append(list(path)) or result.append(path[:]). This round is paired with ML-deployment questions immediately after the coding finishes; budget ≤ 20 minutes here so the deployment discussion has room. Preparation Write both recursive and iterative variants from scratch; the recursive version should fit in 8 lines. Prepare a clean way to format the paths as strings if asked ("1->2->5"), since the LeetCode version returns strings and some interviewers ask for that shape.