Adyen Coding Interview Questions
25 Adyen coding interview problems with full optimal solutions — 11 easy, 11 medium, 3 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Adyen interviewer values, and a FAQ section.
- #1easyfoundational
1. Two Sum
Given an array of integers and a target, return indices of two numbers that sum to the target.
- #2easyfoundational
2. Valid Parentheses
Given a string of brackets, determine if every opener has a matching, properly nested closer.
- #3easyfoundational
3. Merge Two Sorted Lists
Merge two sorted linked lists into a single sorted list in O(n+m).
- #4easyfoundational
4. Remove Duplicates from Sorted Array
Remove duplicates in-place from a sorted array and return the new length.
- #5easyfoundational
5. Best Time to Buy and Sell Stock
Given an array of daily prices, return the maximum profit from one buy and one sell.
- #6easyfoundational
6. Contains Duplicate
Return true if any value appears at least twice in the input array.
- #7easyfoundational
7. Valid Anagram
Given two strings, return true if one is an anagram of the other.
- #8mediumfoundational
8. Maximum Subarray
Find the contiguous subarray with the largest sum and return that sum.
- #9mediumfoundational
9. Group Anagrams
Group strings that are anagrams of each other into the same bucket.
- #10mediumfoundational
10. Top K Frequent Elements
Given an array, return the k most frequent elements.
- #11mediumfoundational
11. Product of Array Except Self
Return an array where each entry is the product of all other entries — no division allowed.
- #12mediumfoundational
12. Longest Consecutive Sequence
Find the length of the longest run of consecutive integers in an unsorted array.
- #13mediumfoundational
13. 3Sum
Find all unique triplets in the array that sum to zero.
- #14mediumfoundational
14. Container With Most Water
Pick two lines forming a container with the x-axis that holds the most water.
- #15mediumfoundational
15. Longest Substring Without Repeating Characters
Find the length of the longest substring without repeating characters.
- #16mediumfoundational
16. Longest Palindromic Substring
Return the longest palindromic substring in the given string.
- #17easyfoundational
17. Reverse Linked List
Given the head of a singly linked list, reverse the list and return the new head.
- #18easyfoundational
18. Linked List Cycle
Detect whether a linked list contains a cycle.
- #19easyfoundational
19. Maximum Depth of Binary Tree
Return the maximum depth of a binary tree.
- #20easyfoundational
20. Invert Binary Tree
Invert a binary tree by swapping every node's left and right children.
- #21mediumfoundational
21. Coin Change
Return the fewest coins needed to make an amount, or -1 if impossible.
- #22mediumfoundational
22. LRU Cache
Design a data structure that supports get and put in O(1) with least-recently-used eviction.
- #23hardfoundational
23. Median of Two Sorted Arrays
Find the median of two sorted arrays in O(log(min(m, n))) time.
- #24hardfoundational
24. Trapping Rain Water
Given an elevation map, compute how much water it traps after raining.
- #25hardfoundational
25. Merge k Sorted Lists
Merge k sorted linked lists into one sorted list.