A problem-first collection of the algorithm questions that dominate technical interviews. Each card is one problem: a precise contract, a small table of worked examples, and a function you implement in Python or C++ against tests that run in the browser. Hints reveal the technique step by step, and the reference solution is one click away when you are stuck.
Volume 1 holds forty-five problems in three decks of fifteen:
- Easy — the warm-ups every interview loop assumes: Two Sum, Contains Duplicate, Valid Anagram, Valid Palindrome, Single Number, Best Time to Buy and Sell Stock, Valid Parentheses, Merge Two Sorted Arrays, Maximum Subarray, Binary Search, Climbing Stairs, plus a first taste of pointers and trees in Reverse Linked List, Merge Two Sorted Lists, Invert Binary Tree and Maximum Depth of Binary Tree.
- Medium — the techniques that separate a pass from a strong pass: hashing (Group Anagrams, Top K Frequent Elements), sliding windows and two pointers (Longest Substring Without Repeating Characters, Container With Most Water, Three Sum), binary search on a rotated array, prefix products, intervals, dynamic programming (Coin Change, House Robber, Longest Increasing Subsequence), selection (Kth Largest Element in an Array), backtracking (Subsets), and graph and grid search (Number of Islands, Course Schedule).
- Hard — the problems interviewers reach for when they want to see you think: Trapping Rain Water, Minimum Window Substring, Sliding Window Maximum, First Missing Positive, Median of Two Sorted Arrays, Edit Distance, Regular Expression Matching, Longest Valid Parentheses, Largest Rectangle in Histogram, Burst Balloons, Merge K Sorted Lists, Word Ladder, Word Search II, N-Queens, and Serialize and Deserialize Binary Tree.
Named techniques — Kadane's algorithm, binary search, two pointers, sliding window, monotonic stacks and deques, backtracking, bottom-up and interval DP — are implemented by hand, not delegated to a library call, because the interview is about the technique. Every reference solution is annotated, and every test suite includes the edge cases (empty input, single element, all-negative, duplicates, ties) that catch a half-right answer.
Later volumes add more problems in the same format; this one is the core set to be fluent in before any interview.