Boundary of Binary Tree

Given the root of a binary tree, return the values of its boundary in anti-clockwise direction starting from the root. Boundary of Binary Tree Given the root of a binary tree, return the values of its boundary in anti-clockwise direction starting from the root. SWE tree dfs tree-traversal medium Frequency Single report Last asked 2025-12-06 Stage phone-screen · onsite-coding Boundary of Binary Tree Problem Requirements You are given the root of a binary tree. Your goal is to return a list of values representing the boundary of the tree. You must trace this boundary in an anti-clockwise (counter-clockwise) direction, starting from the root. The boundary consists of four specific parts: The Root: The top node of the tree. The Left Boundary: The nodes along the left edge. Note: Do not include leaf nodes (nodes with no children) in this part. The Leaves: All the bottom nodes that have no children, listed from left to right. The Right Boundary: The nodes along the right edge. Note: These are added in reverse order (bottom to top) and do not include leaf nodes. Special Rule: If the root node has no left or right subtree (it has no children), then the boundary is just the root itself. Test Cases Case 1: Input: root = [1,null,2,3,4] Output: [1,3,4,2] Case 2: Input: root = [1,2,3,4,5,6,null,null,null,7,8,9,10] Output: [1,2,4,7,8,9,10,6,3] Technical Constraints Tree Size: The number of nodes is between 1 and 10^4 (10,000). Value Range: Each Node.val is between -1000 and 1000.