All Nodes Distance K in Binary Tree
Difficulty: Medium
Category: DSA
Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree
Asked at: Amazon, Facebook, Google
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.
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**Example 2:**
**Input:** root = [1], target = 1, k = 3
**Output:** []
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**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`