How should I practice Vertical Order Traversal of a Binary Tree?

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Problem · Tree

Vertical Order Traversal of a Binary Tree

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Problem statement

Given the root of a binary tree, return its vertical traversal.

Place the root at row 0, column 0. A left child is at (row + 1, column - 1), and a right child is at (row + 1, column + 1).

Return columns from the smallest to the largest column. Within a column, order nodes by row from top to bottom; if multiple nodes share both row and column, order those nodes by value ascending.

Function

verticalTraversal(root: TreeNode) → List<List<Integer>>

Examples

Example 1

root = [3,9,20,null,null,15,7]return = [[9],[3,15],[20],[7]]

The four occupied columns are returned from leftmost to rightmost, with node 15 below the root in column zero.

Example 2

root = [1,2,3,4,5,6,7]return = [[4],[2],[1,5,6],[3],[7]]

Nodes 5 and 6 share row two and column zero, so value order places 5 first.

Example 3

root = [1,2,3,4,6,5,7]return = [[4],[2],[1,5,6],[3],[7]]

Even though traversal reaches 6 before 5, their shared coordinate is sorted by value.

Constraints

The tree contains between 1 and 1000 nodes.
0 <= Node.val <= 1000.