All Nodes Distance K in Binary Tree
A medium-tier problem at 66% community acceptance, tagged with Hash Table, Tree, Depth-First Search. Reported in interviews at DP world and 9 others.
All Nodes Distance K in Binary Tree shows up in live assessments at Meta, Walmart Labs, TikTok, and Salesforce. The problem sounds simple: find all nodes exactly K steps away from a target node in a binary tree. But most candidates get trapped treating it as a pure tree traversal when it's actually a graph problem in disguise. The acceptance rate sits at 66%, which means a solid third of people either time out, mishandle the parent pointers, or botch the distance logic. If this problem hits your assessment and you blank on the two-phase approach, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "All Nodes Distance K in Binary Tree"
All Nodes Distance K in Binary Tree is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too.
Get StealthCoderThe trap: you can't just DFS down from the target node and count steps. You also need to go up through parents and sideways through siblings, which means you need parent pointers that the tree structure doesn't give you. The pattern is build a graph first (using Hash Table to store adjacencies and parent links), then BFS or DFS from the target counting exactly K steps. Most failures come from forgetting the parent direction entirely or confusing distance counting with tree depth. The trick is recognizing this as an undirected-graph shortest-path problem wrapped in tree language. Depth-First Search and Breadth-First Search both work, but BFS with a queue is cleaner for counting exact distances. StealthCoder is your hedge here because the insight takes time to click and you don't have it in a live OA.
Pattern tags
You know the problem.
Make sure you actually pass it.
All Nodes Distance K in Binary Tree recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too. Works on HackerRank, CodeSignal, CoderPad, and Karat.
All Nodes Distance K in Binary Tree interview FAQ
Why can't I just do DFS from the target and return nodes at depth K?+
Because K distance includes going up to ancestors and across to other subtrees. A node K steps away might be in your parent's sibling's subtree. You need bidirectional traversal, which requires treating the tree as an undirected graph with parent pointers first.
Is this really asked at top companies like Meta and Salesforce?+
Yes. It appears in the top company list at 10 organizations including Meta and Walmart Labs. The 66% acceptance rate suggests it's a solid Medium that separates prep from no-prep. Companies use it to test graph thinking in a tree context.
What's the time complexity if I build a parent map first?+
One DFS pass to build the graph with Hash Table is O(N). Then BFS from target is O(N) worst case. Overall O(N), which is optimal. Most failures don't hit the time limit; they fail on logic.
Should I use BFS or DFS from the target after building the graph?+
BFS is safer. You can stop exploring any branch once you hit distance K, avoiding unnecessary recursion. DFS works but you have to be careful not to revisit nodes. Both are O(N), but BFS is cleaner for counting exact distances.
Do I need to handle the case where target is null or K is zero?+
K being zero should return just the target node itself. Target being null is usually not tested, but safe to check. The problem guarantees the target exists in the tree, so focus on the distance logic and parent traversal.
Want the actual problem statement? View "All Nodes Distance K in Binary Tree" on LeetCode →