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Microsoft·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

Microsoft interview focused on a BST successor search problem. Not much context to go on but it reads like a standard technical screen.

Questions Asked (1)

Q1

Given a node in a binary search tree, find its in-order successor.

Algorithms & Data Structures
Author's notes

Classic BST traversal problem but I always second-guess myself on the edge cases.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the definition of in-order successor and the tree structure. Then explain the two cases: if the node has a right subtree, the successor is the leftmost node in that subtree; otherwise, it's the lowest ancestor for which the node is in its left subtree. Provide pseudocode and analyze time and space complexity.

Pro tip: Mention that without parent pointers, finding the successor requires a traversal from the root, but with parent pointers, it can be done in O(h) time without extra space. This shows awareness of practical variations.

1. Clarify the problem

Confirm the definition of in-order successor (next node in in-order traversal) and whether nodes have parent pointers. Also, discuss edge cases like the maximum node having no successor.

2. Explain the algorithm

Describe the two cases: if the node has a right child, go right then leftmost; else, go up until you find a node that is a left child of its parent. If no such ancestor, successor is null.

3. Provide pseudocode

Write clear pseudocode for both cases, handling the absence of parent pointers by keeping track of the ancestor during traversal from the root.

4. Analyze complexity

State that time complexity is O(h) where h is the tree height, and space complexity is O(1) if parent pointers exist, else O(h) for recursion or O(1) for iterative with ancestor tracking.

5. Test with examples

Walk through examples: a node with a right subtree, a leaf node that is a left child, a leaf that is a right child, and the maximum node.

Key Points to Mention

  • In-order successor definition: the next node in the in-order traversal sequence.
  • Case 1: Node has a right subtree → successor is the leftmost node in the right subtree.
  • Case 2: Node has no right subtree → successor is the lowest ancestor whose left subtree contains the node.
  • Handling absence of parent pointers: traverse from root while tracking the potential successor.
  • Time complexity: O(h) where h is the height of the tree; space complexity: O(1) with parent pointers, O(h) without (due to recursion stack) or O(1) iterative.
  • Edge cases: node is the maximum (no successor), node is null, tree is empty.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.