0863. All Nodes Distance K in Binary Tree

https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree

Description

Given the root of a binary tree, the value of a target node target, and an integer k, return an array of the values of all nodes that have a distance k from the target node.

You can return the answer in any order.

Example 1:

**Input:** root = [3,5,1,6,2,0,8,null,null,7,4], target = 5, k = 2
**Output:** [7,4,1]
Explanation: The nodes that are a distance 2 from the target node (with value 5) have values 7, 4, and 1.

Example 2:

**Input:** root = [1], target = 1, k = 3
**Output:** []

Constraints:

• The number of nodes in the tree is in the range [1, 500].

• 0 <= Node.val <= 500

• All the values Node.val are unique.

• target is the value of one of the nodes in the tree.

• 0 <= k <= 1000

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