Spiral Matrix Traversal

Output the elements of an `m × n` matrix in spiral order, walking from the outside layer to the innermost. A warm-up problem in GSAM Infra phone screens. Requirements Input: an m × n matrix. Output: a single list containing every element in spiral order — right across the top, down the right edge, left across the bottom, up the left edge, then inward to the next layer. Notes Maintain four boundary pointers (top, bottom, left, right); contract each one after the corresponding side is consumed. Stop when top > bottom or left > right. The classic off-by-one trap is processing the last single row or column twice when the matrix is non-square — guard the inner two passes with top <= bottom and left <= right. O(m·n) time, O(1) extra space (output array aside). This problem serves as the warm-up before the harder follow-up Maximum-Sum Path in a Matrix in GSAM Infra loops; expect it to be solved in under 10 minutes, leaving room for the second question. Preparation Implement once with explicit boundary pointers; drill the off-by-one cases on a 3×5 and a 5×3 matrix. LC 54 "Spiral Matrix" is the canonical equivalent.