Given a binary tree where every node has a unique value, and a target key k, find the value of the nearest leaf node to target k in the tree. Here, nearest to a leaf means the least number of edges travelled on the binary tree to reach any leaf of the tree. Also, a node is called a leaf if it has no children. In the following examples, the input tree is represented in flattened form row by row. The actual root tree given will be a TreeNode object. Example 1: Input: root = [1, 3, 2], k = 1 Diagram of binary tree: 1 / \ 3 2 Output: 2 (or 3) Explanation: Either 2 or 3 is the nearest leaf node to the target of 1. Example 2: Input: root = [1], k = 1 Output: 1 Explanation: The nearest leaf node is the root node itself. Example 3: Input: root = [1,2,3,4,null,null,null,5,null,6], k = 2 Diagram of binary tree: 1 / \ 2 3 / 4 / 5 / 6 Output: 3 Explanation: The leaf node with value 3 (and not the leaf node with value 6) is nearest to the node with value 2. Note: root represents a binary tree with at least 1 node and at most 1000 nodes. Every node has a unique node.val in range [1, 1000]. There exists some node in the given binary tree for which node.val == k.