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 31 problems of 100
- #1easyfrequently asked
1. Two Sum
Given an array of integers and a target, return indices of the two numbers that add up to the target. Datadog asks this as a warmup but pushes candidates to discuss how the same hashmap pattern scales to streaming pair-detection over high-cardinality metric IDs.
- #2easyfrequently asked
2. Valid Parentheses
Given a string of brackets, determine if every opener has a matching closer in the correct order. Datadog frames this as a streaming log-parser warmup — the same stack discipline shows up when validating JSON log payloads on a high-throughput ingestion pipeline.
- #3easyfrequently asked
3. Merge Two Sorted Lists
Merge two sorted linked lists into one sorted list. Datadog uses this as a stepping stone toward merging K sorted time-series streams — the underlying two-pointer pattern is identical to how their backend stitches ordered metric shards.
- #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.
- #6easyfrequently asked
6. Search Insert Position
Given a sorted array and a target, return the index where the target would be inserted. Datadog uses this as the bedrock for binary-search-on-time questions — every metric query that bisects timestamps uses this pattern.
- #7easyfrequently asked
7. Maximum Subarray
Find the contiguous subarray with the largest sum. Datadog phrases this as 'find the peak metric burst' — Kadane's algorithm runs in a single pass and ports directly to a streaming aggregator over a metric window.
- #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.
- #9easyfrequently asked
9. Merge Sorted Array
Merge two sorted arrays in place, where the first has enough trailing space to hold both. Datadog uses this to test the reverse-iteration trick — the same backward-merge pattern they use when compacting two adjacent TSDB chunks without allocating a third buffer.
- #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.
- #17easyfrequently asked
17. Best Time to Buy and Sell Stock
Find the max profit from one buy and one sell. Datadog frames this as 'find the largest spike in a metric stream' — single pass, constant memory, identical to their min-tracking aggregator.
- #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.
- #19easyfrequently asked
19. Single Number
Every element appears twice except one. Find the singleton in O(n) time and O(1) space. Datadog asks this to test whether you know the XOR trick — a streaming-friendly aggregate that uses constant memory regardless of cardinality.
- #20easyfrequently asked
20. Linked List Cycle
Detect whether a linked list contains a cycle. Datadog uses this as the Floyd-tortoise warmup before more complex cycle-detection problems in their dependency-graph traversals.
- #21easyfrequently asked
21. Min Stack
Design a stack that supports push, pop, top, and getMin all in O(1). Datadog asks this because it's the same shape as a streaming min-aggregate that needs to handle rollbacks (transactional ingestion).
- #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.
- #23easyfrequently asked
23. Majority Element
Find the element that appears more than n/2 times. Datadog asks this because the Boyer-Moore vote algorithm is the canonical streaming-aggregate pattern for finding a heavy hitter in one pass with O(1) memory.
- #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.
- #29easyfrequently asked
29. Reverse Linked List
Reverse a singly linked list. Datadog uses this as the bedrock linked-list question — pointer manipulation here is required for harder problems like reverse-in-groups or merge-k-sorted.
- #30easyfrequently asked
30. Contains Duplicate
Determine if any value appears at least twice in an array. Datadog uses this as the hashset warmup before count-distinct and HyperLogLog discussions for high-cardinality tag streams.
- #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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