Find Nearest Right Node in Binary Tree

Find Nearest Right Node in Binary Tree

What is this problem about?

The Find Nearest Right Node in Binary Tree interview question asks you to find the node that sits immediately to the right of a given target node on the same level of the tree. If the target node is the rightmost node on its level, you should return null. This Find Nearest Right Node coding problem is a test of your ability to traverse a tree level-by-level.

Why is this asked in interviews?

Google asks this to evaluate your knowledge of Breadth-First Search (BFS). Unlike DFS, which goes deep into subtrees, BFS visits nodes in exactly the order needed to find "neighbors" on the same horizontal level. It tests your ability to use a queue and track level boundaries effectively.

Algorithmic pattern used

This problem is best solved using the Level Order Traversal (BFS) pattern.

1. Queue: Use a queue to store nodes for BFS.
2. Level Size: Process nodes level by level by capturing the queue size at the start of each level.
3. Scan: Iterate through the nodes of the current level.
4. Discovery: If you find the target node:
   • If it is not the last node in the current level's processing loop, the next node in the queue is the "nearest right node."
   • If it is the last node, return null.

Example explanation

Tree: 1 is root, 2, 3 are children. 4, 5, 6 are children of 2, 3. Target: 4.

1. Level 0: [1]
2. Level 1: [2, 3]
3. Level 2: [4, 5, 6]
   • Pop 4. Target found!
   • Is there another node in this level? Yes, 5. Result: 5.

Common mistakes candidates make

• DFS Confusion: Trying to use Depth-First Search, which requires tracking depth and finding the "next" node at the same depth—much more complex than BFS.
• Boundary errors: Returning a node from the next level because the logic didn't stop at the end of the current level's size.
• Ignoring Nulls: Not handling empty trees or targets that don't exist.

Interview preparation tip

Master the standard "Level Order Traversal" template using a queue. It is the "gold standard" for any tree problem involving levels, widths, or horizontal neighbors. This is a core Tree interview pattern.