Binary Tree Vertical Order Traversal

Problem Given the root of a binary tree, return its vertical order traversal. Definition: Root has column 0 Left child column = parent column - 1 Right child column = parent column + 1 Output requirements: Columns from leftmost to rightmost Within the same column, order nodes from top to bottom (BFS encounter order) Input format (suggested) Level-order array with null for missing nodes. Constraints Number of nodes N: 0 <= N <= 2e5 Example Input: [3,9,20,null,null,15,7] Output: [[9],[3,15],[20],[7]] Example Input [3,9,20,null,null,15,7] Output [[9],[3,15],[20],[7]]