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.
- #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.
- #31mediumfrequently asked
31. Add Two Numbers
Add two non-negative integers represented as reversed-order linked lists. Datadog uses this to test carry-propagation logic — the same logic as their atomic-counter rollup across pipeline stages.
- #32mediumfrequently asked
32. Longest Substring Without Repeating Characters
Find the length of the longest substring with no repeating characters. Datadog asks this as the sliding-window foundation — the same pattern they use for windowed deduplication of streaming events.
- #33mediumsometimes asked
33. Longest Palindromic Substring
Find the longest palindromic substring. Datadog asks this for the expand-around-center pattern — O(n^2) time with O(1) space, a sweet spot for streaming validators that can't afford O(n) extra memory.
- #34mediumsometimes asked
34. Container With Most Water
Find two heights that form a container holding the most water. Datadog asks this for the two-pointer-greedy proof — the same kind of monotone-invariant reasoning needed for windowed peak detection on metric streams.
- #35mediumfrequently asked
35. 3Sum
Find all unique triplets that sum to zero. Datadog uses this as the cornerstone two-pointer + dedup question — the same pattern needed for finding triple-correlations in cross-metric anomaly detection.
- #36mediumsometimes asked
36. Letter Combinations of a Phone Number
Generate all possible letter combinations for a phone-keypad number. Datadog uses this as a backtracking warmup — same recursive-emission structure as their downsampling rollup that enumerates resolution buckets.
- #37mediumsometimes asked
37. Remove Nth Node From End of List
Remove the Nth-from-end node in a singly linked list in one pass. Datadog tests the two-pointer-offset trick — the same pattern they use to maintain a fixed-lag window over a streaming sequence.
- #38mediumsometimes asked
38. Generate Parentheses
Generate all combinations of n well-formed parentheses. Datadog asks this for the backtracking constraint-pruning pattern — the same idea applied to enumerating valid log-parser states.
- #39mediumrarely asked
39. Swap Nodes in Pairs
Swap every two adjacent nodes in a linked list, in place. Datadog uses this to test pointer-manipulation discipline before harder variants like reverse-in-groups.
- #40mediumrarely asked
40. Next Permutation
Rearrange numbers into the lexicographically next greater permutation. Datadog uses this as a deep array-manipulation question — the algorithmic clarity is similar to the cursor-advance logic in their iterator-based query layer.
- #41mediumfrequently asked
41. Search in Rotated Sorted Array
Search for a target in a rotated sorted array in O(log n). Datadog asks this because their TSDB indexes can be rotated chunks (after compaction crosses a boundary), and bisect must still work correctly.
- #42mediumfrequently asked
42. Find First and Last Position of Element in Sorted Array
Find the first and last index of a target in a sorted array using O(log n). Datadog asks this because their TSDB needs range-bisect (start and end of a value range) for every query that filters by timestamp.
- #43mediumrarely asked
43. Valid Sudoku
Validate a 9x9 Sudoku board against the row/col/box rules in a single pass. Datadog asks this because the constraint-encoding trick (one Set per row/col/box) is the same shape as validating multi-dimensional metric tags in a single ingestion pass.
- #44mediumsometimes asked
44. Combination Sum
Find all unique combinations of candidate integers that sum to target, with reuse allowed. Datadog asks this for the backtracking-with-reuse pattern — same shape as expanding multi-resolution rollup partitions.
- #45mediumsometimes asked
45. Permutations
Generate all permutations of a distinct-integer array. Datadog uses this as a baseline backtracking question — and follows up by asking how to lazily yield permutations as an iterator over a streaming consumer.
- #46mediumsometimes asked
46. Rotate Image
Rotate an N x N matrix 90 degrees clockwise in place. Datadog tests this for the transpose-plus-reverse trick — same shape as their column-store to row-store flip during chunk compaction.
- #47mediumfrequently asked
47. Group Anagrams
Group strings that are anagrams of each other. Datadog asks this because the canonicalize-then-hash pattern is identical to how they group equivalent metric series by sorted-tag-keys for query deduplication.
- #48mediumrarely asked
48. Spiral Matrix
Traverse an M x N matrix in spiral (clockwise) order. Datadog uses this as a 2D-traversal warmup to test boundary-management discipline — the same shape as iterating over a chunked time-series block with varying boundaries.
- #49mediumfrequently asked
49. Jump Game
Determine if you can reach the last index given an array of max jump lengths. Datadog asks this for the greedy max-reach pattern — same shape as a streaming reachability check over a partially-observed graph.
- #50mediumfrequently asked
50. Merge Intervals
Merge all overlapping intervals. Datadog asks this constantly because it's the foundation of compaction — merging overlapping metric chunks, log batches, or active session windows is the same problem.
- #51mediumsometimes asked
51. Unique Paths
Count paths from top-left to bottom-right of an m x n grid, moving only right or down. Datadog asks this as a DP-fundamentals warmup before harder grid problems with constraints.
- #52mediumsometimes asked
52. Minimum Path Sum
Find the minimum-cost path from top-left to bottom-right of a grid, moving only right or down. Datadog uses this as a weighted-DP foundation before harder pathfinding questions.
- #53mediumsometimes asked
53. Simplify Path
Convert a Unix-style absolute path into its canonical form. Datadog uses this for the stack-based path-segment pattern — same shape as their tag-prefix normalization for hierarchical metric names.
- #54mediumsometimes asked
54. Edit Distance
Compute the minimum number of insert/delete/replace operations to convert one string into another (Levenshtein distance). Datadog asks this for the classic 2D DP — same recurrence they use when diffing two metric-name versions during schema migration.
- #55mediumrarely asked
55. Set Matrix Zeroes
Given an m x n matrix, if an element is 0, set its entire row and column to 0 — in place, O(1) extra space. Datadog asks this for the encode-state-in-matrix trick — same shape as their in-place chunk-level invalidation marks during compaction.
- #56mediumsometimes asked
56. Search a 2D Matrix
Search for a target in a row-sorted matrix where the first element of each row > the last element of the previous row. Datadog asks this to verify you spot the flatten-to-1D trick — same shape as indexing a packed sorted block as if it were a flat array.
- #57mediumfrequently asked
57. Sort Colors
Sort an array of 0s, 1s, and 2s in place in one pass. Datadog asks this as the canonical Dutch National Flag warmup — same three-way-partition trick they use for tagging metric series by priority.
- #58mediumsometimes asked
58. Subsets
Return all subsets of a distinct-integer array (the power set). Datadog uses this as a backtracking foundation, and probes you to discuss bitmask enumeration as an alternative.
- #59mediumsometimes asked
59. Word Search
Determine if a word exists in a 2D board where adjacent cells form a path. Datadog uses this for the DFS-with-backtracking pattern — same shape as searching for a metric-name pattern in a hierarchical store.
- #60mediumsometimes asked
60. Decode Ways
Count the number of ways to decode a digit string into letters (A=1, B=2, ..., Z=26). Datadog asks this for the 1D DP pattern — same shape as their dynamic-parser that branches on ambiguous log-line prefixes.
- #61mediumfrequently asked
61. Validate Binary Search Tree
Determine if a binary tree satisfies BST properties. Datadog asks this for the bounds-passing recursion pattern — same shape as validating an ordered range invariant on a hierarchical metric store.
- #62mediumfrequently asked
62. Binary Tree Level Order Traversal
Return a binary tree's level-order traversal grouped by level. Datadog uses this as the BFS-foundation question — same level-batched pattern they use for paginated tree expansion in their query layer.
- #63mediumsometimes asked
63. Binary Tree Zigzag Level Order Traversal
Return a binary tree's level-order traversal but alternate left-to-right and right-to-left per level. Datadog uses this BFS variant to test that you can compose direction-flipping on top of the level-batch primitive.
- #64mediumsometimes asked
64. Construct Binary Tree from Preorder and Inorder Traversal
Reconstruct a binary tree given its preorder and inorder traversals. Datadog uses this to test the divide-and-conquer recursion pattern with O(1) lookups via a position index — same shape as deserialization in their distributed metric storage layer.
- #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.
- #66mediumsometimes asked
66. Path Sum II
Find all root-to-leaf paths where the sum equals a target. Datadog uses this for backtracking with path tracking — same shape as enumerating valid traces through a service-dependency graph.
- #67hardsometimes asked
67. Word Ladder
Find the shortest transformation sequence from beginWord to endWord, changing one letter at a time, using only words from a dictionary. Datadog uses this as a BFS-on-implicit-graph question — same pattern they use for shortest-path queries on dynamic service topologies.
- #68mediumfrequently asked
68. Longest Consecutive Sequence
Find the longest sequence of consecutive integers in an unsorted array in O(n). Datadog asks this for the start-only expansion trick — same pattern as compacting consecutive timestamps in a sparse metric block.
- #69mediumsometimes asked
69. Copy List with Random Pointer
Deep-copy a linked list where each node has both a next pointer and a random pointer to any node. Datadog uses this for the old-to-new mapping trick — same shape as their snapshot logic for a graph with arbitrary edges.
- #70mediumsometimes asked
70. Word Break
Given a string and a dictionary, determine if the string can be segmented into a sequence of dictionary words. Datadog uses this for the 1D DP segmentation pattern — same shape as their tokenizer for tag-pattern matching on hierarchical metric names.
- #71mediumfrequently asked
71. LRU Cache
Design a cache with get and put operations in O(1). Datadog asks this constantly — every metric ingestion pipeline has an LRU at some boundary for resolving high-cardinality tag IDs to interned values.
- #72mediumsometimes asked
72. Sort List
Sort a linked list in O(n log n) time and O(1) extra space. Datadog asks this for the bottom-up merge-sort pattern — same shape as their external-sort routine over chunked metric files.
- #73mediumsometimes asked
73. Maximum Product Subarray
Find the contiguous subarray with the largest product. Datadog asks this for the dual-track DP trick (track both min and max) — same shape as anomaly detection that must handle bidirectional outliers.
- #74mediumfrequently asked
74. Find Minimum in Rotated Sorted Array
Find the minimum value in a rotated sorted array in O(log n). Datadog asks this because their TSDB rotates compacted chunks across the time axis, and locating the pivot is the prerequisite for any range query.
- #75mediumsometimes asked
75. Find Peak Element
Find any peak element in O(log n). Datadog asks this for the non-monotonic binary-search pattern — peak detection in metric streams uses the same uphill-direction logic.
- #76mediumsometimes asked
76. Find the Duplicate Number
Find the single duplicate in an array of n+1 integers where each is in [1, n]. Datadog asks this for the Floyd-tortoise-on-implicit-cycle trick — finding a duplicate metric ID in O(n) time, O(1) memory.
- #77mediumfrequently asked
77. Kth Largest Element in an Array
Find the kth largest element in an unsorted array. Datadog asks this for the min-heap-of-size-k trick — same streaming aggregate they use to maintain top-K leaderboards over high-cardinality metric streams.
- #78mediumfrequently asked
78. Course Schedule
Determine if you can finish all courses given prerequisite pairs — equivalent to detecting a cycle in a directed graph. Datadog asks this because their dashboard-dependency graph and metric-rollup DAG must remain acyclic.
- #79mediumfrequently asked
79. Implement Trie (Prefix Tree)
Implement a Trie with insert, search, and startsWith. Datadog uses this as the gateway to prefix-search problems — same shape as their tag-name autocomplete that serves their high-cardinality search UI.
- #80mediumfrequently asked
80. Minimum Size Subarray Sum
Find the minimum length contiguous subarray whose sum is at least target. Datadog asks this for the variable-size sliding-window pattern — same shape as their alert-window optimization over a metric stream.
- #81mediumfrequently asked
81. Number of Islands
Count connected components of '1's in a 2D grid. Datadog uses this as the canonical grid-BFS/DFS question — same shape as counting active service clusters in a service-mesh observability view.
- #82mediumsometimes asked
82. House Robber
Max-sum subsequence with no two adjacent elements. Datadog uses this as the simplest 1D DP question — same shape as their non-overlapping window aggregation over a metric stream.
- #83mediumfrequently asked
83. Coin Change
Find the minimum number of coins to make a target amount. Datadog asks this for the unbounded-knapsack DP pattern — same shape as their resolution-stitching algorithm that selects the minimum number of pre-aggregated buckets to cover a query window.
- #84mediumfrequently asked
84. Longest Increasing Subsequence
Find the length of the longest strictly increasing subsequence. Datadog asks this for the patience-sorting O(n log n) trick — same shape as their monotonic-history compression for time-series anomaly trend detection.
- #85mediumfrequently asked
85. Top K Frequent Elements
Return the k most frequent elements. Datadog asks this for the heap-of-size-k + bucket-sort alternative — same shape as their top-K leaderboard for hottest metric series in a high-cardinality stream.
- #86mediumsometimes asked
86. Design Add and Search Words Data Structure
Design a dictionary with addWord and search where '.' matches any letter. Datadog uses this for the Trie + DFS combo — same shape as their wildcard-tag-pattern lookup in the metric query layer.
- #87hardfrequently asked
87. Serialize and Deserialize Binary Tree
Design serialize and deserialize for an arbitrary binary tree. Datadog uses this as the canonical wire-format question — same shape as their distributed metric-tree snapshot format that flows between ingest and query nodes.
- #88hardfrequently asked
88. Find Median from Data Stream
Design addNum and findMedian over a streaming sequence. Datadog asks this as the canonical streaming-percentile problem — two-heap solution is the exact pattern they use for p50 over a sliding metric window.
- #89hardfrequently asked
89. Sliding Window Maximum
Return the max of each sliding window of size k. Datadog asks this constantly — the monotonic deque is the exact algorithm they use for streaming max-over-window aggregations on real-time metric dashboards.
- #90hardsometimes asked
90. Median of Two Sorted Arrays
Find the median of two sorted arrays in O(log(min(m,n))). Datadog asks this for the partition-based binary search — same shape as quantile estimation over two pre-aggregated metric blocks.
- #91hardsometimes asked
91. Regular Expression Matching
Implement regex matching with '.' and '*'. Datadog asks this as a hard DP — same shape as their tag-pattern engine that matches user-specified wildcards against high-cardinality metric names.
- #92hardfrequently asked
92. Merge k Sorted Lists
Merge k sorted linked lists into one sorted list. Datadog asks this because their query layer routinely merges K ordered metric shards into a unified stream — the min-heap pattern is identical.
- #93hardsometimes asked
93. Reverse Nodes in k-Group
Reverse linked list nodes in groups of K, leaving the tail intact if it's shorter than K. Datadog uses this to test deep pointer manipulation — same shape as in-place chunk reversal in their reverse-time-order query optimization.
- #94hardrarely asked
94. Substring with Concatenation of All Words
Find all starting indices of substrings that are a concatenation of each word exactly once. Datadog asks this for the hash-based sliding window — same shape as multi-tag-pattern detection on a log stream.
- #95hardrarely asked
95. Longest Valid Parentheses
Find the length of the longest valid (well-formed) parentheses substring. Datadog uses this for the stack-tracking-indices trick — same shape as their balanced-segment detector on partially-corrupted log streams.
- #96hardrarely asked
96. Sudoku Solver
Solve a 9x9 Sudoku via backtracking. Datadog uses this as a deep constraint-satisfaction question — same shape as their resource-allocation solver that fills a constrained schedule.
- #97hardsometimes asked
97. First Missing Positive
Find the smallest missing positive integer in O(n) time and O(1) space. Datadog uses this for the index-as-hash trick — same shape as their dense-key occupancy check across a metric-ID space.
- #98hardfrequently asked
98. Trapping Rain Water
Compute how much water gets trapped between bars. Datadog uses this for the two-pointer greedy proof — same shape as bounded peak-valley estimation in a streaming metric series.
- #99hardrarely asked
99. N-Queens
Place N queens on an N x N board such that none attack each other. Datadog uses this as the canonical backtracking + constraint encoding question — same shape as multi-dim CSP they use for capacity placement.
- #100hardfrequently asked
100. Largest Rectangle in Histogram
Find the largest rectangle area in a histogram. Datadog uses this for the monotonic-stack pattern — same shape as their algorithm for detecting the largest sustained burst window in a metric stream.
Related interview-prep guides
Beyz AI Alternatives in 2026: 7 Tools Compared (Screenshot + Stealth Helpers)
Beyz AI is a screenshot-and-clipboard interview helper that surfaces AI answers on a hidden overlay during online assessments and live rounds. The 2026 reality: candidates search for alternatives because of detection anxiety on monitored OAs, the $30+/month price tag with feature ceilings, and the narrow scope (coding-OA-shaped use only). This guide ranks the 7 best Beyz AI alternatives in the same screenshot-helper category, with InterviewChamp.AI compared honestly alongside, plus how to pick based on your specific interview gauntlet.