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742. Closest Leaf in a Binary Tree

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Description

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:

1. root represents a binary tree with at least 1 node and at most 1000 nodes.
2. Every node has a unique node.val in range [1, 1000].
3. There exists some node in the given binary tree for which node.val == k.

Solutions

Python3

Java

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