Is All Nodes Distance K in Binary Tree easy or hard?

All Nodes Distance K in Binary Tree is classified as a Medium difficulty problem. The core challenge is recognizing that traversal must go both downward and upward from the target. Once the tree is treated like an undirected graph, a standard BFS level traversal solves it efficiently.

How to solve All Nodes Distance K in Binary Tree in O(n)?

Traverse the tree once to record parent pointers for every node. Then perform a BFS starting from the target node while expanding to its left child, right child, and parent. Track visited nodes to avoid cycles and stop when the BFS level equals k. The nodes in that level form the result, giving an overall O(n) solution.

All Nodes Distance K in Binary Tree Python or Java solution

In Python or Java, the typical implementation builds a HashMap or dictionary mapping each node to its parent, then runs a BFS using a queue starting from the target node. Each BFS level represents one edge distance. Once the level equals k, collect the node values and return them.

What is the best approach for All Nodes Distance K in Binary Tree?

The most common solution uses Breadth-First Search with a parent map. First build a mapping from each node to its parent, then start a BFS from the target node and explore left, right, and parent neighbors. When the BFS reaches distance k, all nodes at that level are the answer. This approach runs in O(n) time and O(n) space.

What data structure is used in All Nodes Distance K in Binary Tree?

The common solution uses a hash map to store parent pointers and a queue for Breadth-First Search. A visited set prevents revisiting nodes when moving between parent and child links. The alternative DFS solution relies on recursion and distance propagation during backtracking.

What is the time complexity of All Nodes Distance K in Binary Tree?

The optimal solutions run in O(n) time where n is the number of nodes in the tree. Each node is visited at most once either during the parent map construction or the traversal that finds nodes at distance k. Space complexity is O(n) for the BFS approach or O(h) for the DFS backtracking approach, where h is the tree height.

Is All Nodes Distance K in Binary Tree asked at Google Amazon or Meta?

This problem is a classic binary tree traversal question frequently asked in technical interviews at large companies including Google, Amazon, and Meta. It tests understanding of tree traversal, BFS levels, and how to convert a tree into a graph-like structure using parent references.

Description Solution Video 21:59

863. All Nodes Distance K in Binary Tree

Medium68.1% acceptance16 companies

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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863. All Nodes Distance K in Binary Tree

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