Flatten Nested Array

Flatten a nested array structure into a single list while preserving left-to-right order. Examples Example 1: Input: nested = [[1, 2, 3], [4, 5], [6]] Output: [1, 2, 3, 4, 5, 6] Explanation: Each sub-array is concatenated in order. Example 2: Input: nested = [[1], [], [2, 3]] Output: [1, 2, 3] Explanation: Empty sub-arrays contribute nothing. Example 3: Input: nested = [] Output: [] Constraints 0 <= nested.length <= 10^4 Leaves are 32-bit signed integers. The grader uses depth-2 inputs (number[][]); your recursive solution should still generalize to arbitrary depth — that is what the interviewer evaluates.