Online assessment
Spotify Coding Questions
Overview
Practice Spotify coding questions in the style students report for online assessments and technical interviews. Focus areas: DSA, distributed systems, backend. Languages commonly allowed: Java, Python, Scala.
Spotify coding pattern
| Item | Typical expectation |
|---|---|
| Problems | 1-3 coding tasks depending on drive |
| Skills | DSA, distributed systems, backend |
| Languages | Java, Python, Scala (use what the assessment email lists) |
| What matters | Correctness first, then speed and clear code |
Practice problems
Question 1: move zeros
Coding Q1: Move zeros
Problem: Move all zeros in an array to the end while keeping the relative order of non-zero elements.
Approach: Two pointers: write non-zeros toward the front, then fill the remainder with zeros. Or swap zeros as you scan.
Complexity: O(n) time, O(1) space
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 2: rotate array
Coding Q2: Rotate array
Problem: Rotate an array to the right by k steps. Example: [1,2,3,4,5,6,7], k = 3 → [5,6,7,1,2,3,4].
Approach: Normalize k %= n. Reverse the whole array, reverse the first k elements, then reverse the rest. That yields the rotation in place.
Complexity: O(n) time, O(1) space
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 3: first unique character
Coding Q3: First unique character
Problem: Find the first non-repeating character in a string and return its index, or -1 if none exists.
Approach: Count frequencies in one pass (hash map or array of 26 for lowercase). Second pass returns the first index with count 1.
Complexity: O(n) time
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 4: stack with min
Coding Q4: Stack with min
Problem: Design a stack that supports push, pop, top, and getMin in average O(1) time.
Approach: Keep a parallel min-stack (or store pairs). When pushing, also push the new minimum. When popping, pop both stacks.
Complexity: O(1) per operation amortized
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 5: maximum subarray sum
Coding Q5: Maximum subarray sum (Kadane)
Problem: Given an integer array, find the contiguous subarray with the largest sum and return that sum. Example: [-2,1,-3,4,-1,2,1,-5,4] → 6 (from [4,-1,2,1]).
Approach: Keep a running sum. If the running sum drops below 0, reset it to 0 before taking the next element (or track the best ending-here value). Track the global maximum as you scan once from left to right.
Complexity: O(n) time, O(1) extra space
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 6: reverse a string in place
Coding Q6: Reverse a string in place
Problem: Given a mutable character array representing a string, reverse it in place without allocating another array of the same size.
Approach: Use two pointers at the start and end. Swap characters, then move inward until the pointers meet. Watch empty and single-character inputs.
Complexity: O(n) time, O(1) extra space
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 7: check prime
Coding Q7: Check prime
Problem: Write a function that returns true if n is prime and false otherwise. Handle n < 2 correctly.
Approach: Return false for n < 2. Trial-divide from 2 to floor(sqrt(n)). If any divisor divides n evenly, it is composite; otherwise prime.
Complexity: O(√n) time
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 8: valid parentheses
Coding Q8: Valid parentheses
Problem: Given a string containing only ‘()[]’, decide whether the brackets are balanced and correctly nested.
Approach: Scan left to right with a stack. Push opening brackets. On a closing bracket, the stack top must be the matching opener. At the end the stack must be empty.
Complexity: O(n) time, O(n) space
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 9: two sum
Coding Q9: Two Sum
Problem: Given an array of integers and a target, return indices of two numbers that add up to the target. Assume exactly one solution and you may not use the same element twice.
Approach: Walk the array once. For each value x, check whether target − x was seen earlier in a hash map of value → index. If yes, return both indices; else store x.
Complexity: O(n) time, O(n) space
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Question 10: longest substring without repeating characters
Coding Q10: Longest substring without repeating characters
Problem: Given a string s, find the length of the longest substring without repeating characters. Example: ‘abcabcbb’ → 3 (‘abc’).
Approach: Sliding window with a map (or last-seen index) of characters. Expand the right pointer; when a duplicate appears inside the window, move the left pointer past the previous occurrence.
Complexity: O(n) time
Spotify tip: Restate the problem, sketch a brute-force idea, then tighten it. Call out edge cases (empty input, single element, overflow) before you write code.
Pattern drill plan (2 weeks)
| Day | Drill |
|---|---|
| Mon | Arrays + hashing (2 problems) |
| Tue | Two pointers / sliding window |
| Wed | Stacks / strings |
| Thu | Trees or graphs basics |
| Fri | Timed mock (1-2 problems) |
| Sat | Re-solve misses cold |
| Sun | Explain your project out loud + rest |