Datadog Coding Interview Questions
100 Datadog coding interview problems with full optimal solutions — 31 easy, 54 medium, 15 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Datadog interviewer values, and a FAQ section.
Showing 18 problems of 100
- #4easysometimes asked
4. Remove Duplicates from Sorted Array
Given a sorted array, remove duplicates in place and return the new length. Datadog uses this to test two-pointer mechanics — the same pattern they use for compacting sorted metric chunks before compression.
- #5easysometimes asked
5. Remove Element
Given an array and a value, remove all occurrences in place and return the new length. Datadog uses this as a hello-world for in-place stream filtering — same pattern as their per-tag drop-rule applied to incoming logs.
- #8easysometimes asked
8. Plus One
Given an array of digits representing an integer, increment by one and return the new digit array. Datadog uses this to gauge edge-case discipline — the 999 → 1000 case is the same shape as carry propagation in their atomic-counter rollup.
- #10easysometimes asked
10. Binary Tree Inorder Traversal
Return the inorder traversal of a binary tree's node values. Datadog asks this to test whether you can convert recursion to an explicit stack — the iterative form is required for traversing on-disk tree-indexed metric blocks where the recursion depth would blow the stack.
- #11easysometimes asked
11. Same Tree
Given two binary trees, determine if they are structurally identical with equal node values. Datadog asks this as a baseline tree-recursion question — and follows up by asking how you'd compare two ingestion-state snapshots for drift.
- #12easysometimes asked
12. Symmetric Tree
Check whether a binary tree is a mirror of itself (symmetric around its center). Datadog likes this as a paired-recursion warmup — same shape as comparing the inbound vs outbound side of a bidirectional metric pipeline.
- #13easysometimes asked
13. Maximum Depth of Binary Tree
Return the maximum depth of a binary tree. Datadog uses this as the simplest height question and then escalates to bounded-memory variants for trees stored on disk in chunked form.
- #14easysometimes asked
14. Balanced Binary Tree
Determine if a binary tree is height-balanced. Datadog asks this to test the post-order single-pass trick — return both balance status and height up the stack, avoiding O(n^2) recomputation.
- #15easysometimes asked
15. Minimum Depth of Binary Tree
Return the minimum depth — the shortest path from root to a leaf. Datadog uses this as a BFS-vs-DFS tradeoff question: DFS visits every node, BFS short-circuits at the first leaf.
- #16easyrarely asked
16. Pascal's Triangle
Generate the first N rows of Pascal's triangle. Datadog uses this as a simple DP warmup — each row depends only on the previous, the same shape as rolling-window aggregates over consecutive minutes.
- #18easysometimes asked
18. Valid Palindrome
Determine if a string is a palindrome, considering only alphanumeric characters and ignoring case. Datadog uses this as a two-pointer warmup before harder string-stream problems.
- #22easysometimes asked
22. Two Sum II - Input Array Is Sorted
Find two numbers in a sorted array that add up to a target — using O(1) memory. Datadog uses the two-pointer trick as a building block for problems on sorted metric streams where allocating a hashmap is wasteful.
- #24easysometimes asked
24. Rotate Array
Rotate an array to the right by k steps. Datadog asks this for the in-place reversal trick — same pattern as cyclically rotating a fixed-size ring buffer in their ingest pipeline.
- #25easyrarely asked
25. Reverse Bits
Reverse the bits of a 32-bit unsigned integer. Datadog uses this to test bit-twiddling and the cached-lookup-table trick — exactly the pattern they use for hash-mixing in their high-cardinality tag IDs.
- #26easysometimes asked
26. Number of 1 Bits
Count the number of 1-bits in an unsigned 32-bit integer (popcount). Datadog asks this for the Brian Kernighan trick — used in their bitmap-based tag-presence checks where popcount is in the hot path.
- #27easyrarely asked
27. Happy Number
Determine if a number is 'happy' — repeated sum of squares of digits eventually reaches 1. Datadog asks this as a cycle-detection-on-implicit-graphs question, where Floyd's algorithm applies even without a literal linked list.
- #28easyrarely asked
28. Isomorphic Strings
Determine if two strings are isomorphic — every character in s maps to one in t under a consistent 1-to-1 substitution. Datadog asks this for the two-way-mapping insight — same shape as their tag-name canonicalization on ingest.
- #65easysometimes asked
65. Convert Sorted Array to Binary Search Tree
Convert a sorted array into a height-balanced BST. Datadog uses this for the recursive midpoint split — same pattern they use when bulk-loading an ordered chunk into a balanced index tree.
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