Microsoft Coding Interview Questions
20 Microsoft coding interview problems with full optimal solutions — 5 easy, 13 medium, 2 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Microsoft interviewer values, and a FAQ section.
Showing 20 problems of 20
- #20easyfoundational
20. Valid Parentheses
Valid Parentheses is the Microsoft warm-up that tests whether you can pick the right data structure on the first try. The answer is always a stack — explain why before writing code, and use a closing-to-opening hash map so the matching logic is a single comparison.
4 free resourcesSolve → - #42hardfrequently asked
42. Trapping Rain Water
Trapping Rain Water is the Microsoft hard that separates the two-pointer fluent from the rest. Naive answer is O(n^2). DP with leftMax/rightMax arrays is O(n) time + O(n) space. The two-pointer version is O(n) time + O(1) space — the bonus the interviewer is hoping you reach.
4 free resourcesSolve → - #46mediumfrequently asked
46. Permutations
Permutations is Microsoft's introduction to backtracking. Given distinct integers, generate every ordering. The standard template — pick, recurse, unpick — is what the interviewer is grading; the in-place swap variant is the bonus answer for the same complexity in less memory.
4 free resourcesSolve → - #54mediumfrequently asked
54. Spiral Matrix
Spiral Matrix is Microsoft's most-asked matrix-traversal question. The interviewer is grading whether you can manage four shrinking boundaries (top, bottom, left, right) without an off-by-one bug at the moment two boundaries cross in the middle of a row or column.
4 free resourcesSolve → - #56mediumfrequently asked
56. Merge Intervals
Merge Intervals is the Microsoft sort-then-sweep classic. Sort intervals by start, then walk left to right merging into the previous interval whenever the current start is <= previous end. The interviewer wants you to name 'sort plus single pass' as the structure before coding.
4 free resourcesSolve → - #98mediumfrequently asked
98. Validate Binary Search Tree
Validate Binary Search Tree is the classic Microsoft tree question that punishes the obvious-but-wrong solution: comparing each node only to its immediate children. The interviewer wants the (min, max) bounds recursion or the in-order traversal, and grades the failure case you missed.
4 free resourcesSolve → - #103mediumfrequently asked
103. Binary Tree Zigzag Level Order Traversal
Binary Tree Zigzag Level Order Traversal is Microsoft's BFS-with-a-twist medium. Do a normal level-order BFS, then reverse alternate levels at the end. The cleaner trick is using a deque-as-output and toggling push direction every level.
4 free resourcesSolve → - #138mediumfrequently asked
138. Copy List with Random Pointer
Copy List with Random Pointer is Microsoft's classic deep-clone test. The trick is mapping each original node to its clone so the random pointer (which might point forward into yet-uncloned territory) lands on the right copy. Two passes with a hash map is the standard answer; O(1) space with interleaving is the bonus.
4 free resourcesSolve → - #139mediumfrequently asked
139. Word Break
Word Break is Microsoft's introduction to dynamic programming on strings. The dp[i] = 'is s[0..i] segmentable' framing turns an exponential recursion into a linear-in-n^2 fill. Interviewers want to see you reject memoized DFS as a path to the same answer.
4 free resourcesSolve → - #151mediumfrequently asked
151. Reverse Words in a String
Reverse Words in a String is Microsoft's go-to string-manipulation question. The clean two-liner (split, reverse, filter, join) is acceptable but interviewers grade highly on the in-place O(1) version that reverses the whole string then reverses each word.
4 free resourcesSolve → - #168easyfrequently asked
168. Excel Sheet Column Title
Excel Sheet Column Title is Microsoft's deliberately-off-by-one base-26 puzzle. Excel columns A..Z, AA..AZ, BA.. are 1-indexed with no zero digit, so a vanilla base-26 conversion is wrong. The fix is subtracting one before every modulo.
4 free resourcesSolve → - #202easyfrequently asked
202. Happy Number
Happy Number is Microsoft's favorite cycle-detection question disguised as math. The trick is recognizing the digit-square sum sequence either reaches 1 or enters a cycle — so Floyd's tortoise-and-hare applies and the space drops to O(1).
4 free resourcesSolve → - #206easyfoundational
206. Reverse Linked List
Reverse Linked List is Microsoft's go-to pointer-manipulation warm-up. Interviewers want you to talk through the three-pointer dance (prev, curr, next) without losing the rest of the list and to mention the recursive variant before they ask.
4 free resourcesSolve → - #207mediumfrequently asked
207. Course Schedule
Course Schedule is Microsoft's cycle-detection-on-a-directed-graph staple. The question is 'can you finish all courses' which reduces to 'is the prereq graph a DAG.' Two valid answers — DFS with three-state coloring or Kahn's BFS — both score full marks if you can articulate why.
4 free resourcesSolve → - #208mediumfrequently asked
208. Implement Trie (Prefix Tree)
Implement Trie is the Microsoft data-structure design medium. The clean answer is a node class with a children object and an isEnd flag. Microsoft cares that you can write insert, search, and startsWith without mixing them up — they share traversal logic but stop on different conditions.
4 free resourcesSolve → - #277mediumfrequently asked
277. Find the Celebrity
Find the Celebrity is Microsoft's elegant elimination puzzle. With n people and a knows(a,b) oracle, brute force is O(n^2). The two-pointer elimination trick gets it to O(n) calls — and the verification pass is what makes the candidate proof bulletproof.
4 free resourcesSolve → - #297hardfrequently asked
297. Serialize and Deserialize Binary Tree
Serialize and Deserialize Binary Tree is Microsoft's litmus test for whether you can design a custom encoding and parse it back. The pre-order DFS with explicit null markers is the standard answer; the interviewer is grading whether your serializer and deserializer agree on exactly how nulls are represented.
4 free resourcesSolve → - #380mediumfrequently asked
380. Insert Delete GetRandom O(1)
Insert Delete GetRandom O(1) is Microsoft's go-to data-structure design medium. The trick is pairing an array (for O(1) random access by index) with a hash map (for O(1) value lookup), then doing the swap-with-last trick on delete.
4 free resourcesSolve → - #438mediumfrequently asked
438. Find All Anagrams in a String
Find All Anagrams in a String is Microsoft's clean sliding-window-with-frequency-matching question. Maintain a window of length p over s; compare frequencies on each slide. The clever variant — track only a diff counter instead of comparing maps — is the optimization Microsoft hopes you reach.
4 free resourcesSolve → - #703easyfrequently asked
703. Kth Largest Element in a Stream
Kth Largest Element in a Stream is Microsoft's go-to question for whether you reach for the right data structure when 'streaming' enters the problem. The answer is a min-heap of size k — anything else (sorted list, max-heap) has the wrong asymptotic cost.
4 free resourcesSolve →
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