Coding Interview Prep: DSA/SQL

Coding interview prep for the questions that actually come up: data structures and algorithms, SQL interview questions and competitive programming, in three tracks with 90 short courses and 360 lessons. Learn a pattern, answer the question behind it, then write the solution in Python and run it.

A coding interview is not a memory test. The interviewer wants to hear why one working answer beats another. The app starts with exactly that: one real question, Two Sum, and two correct solutions running side by side on the same 64 numbers, with every comparison counted on your screen. Same answer, far more work. That gap is what big O notation and time complexity are about.

THREE TRACKS, 90 COURSES
• Data Structures & Algorithms: complexity, arrays and two pointers, strings, sorting, binary search, linked lists, stacks and queues, hash maps, recursion, trees, heaps, graphs with BFS and DFS, backtracking, greedy algorithms, dynamic programming, shortest paths, tries, union-find, bit manipulation and system design basics
• SQL for interviews: SELECT and WHERE gotchas, top-N questions, GROUP BY and HAVING, every kind of JOIN, NULL handling, subqueries and CTEs, window functions (ROW_NUMBER, RANK, LAG, LEAD), gaps and islands, cohort and funnel analysis, EXPLAIN and indexing, transactions, schema design
• Competitive Programming: online judges and verdicts, fast input and output, "will it pass" estimates, prefix sums, complete search, number theory and combinatorics, advanced DP, Dijkstra, Fenwick and segment trees, string algorithms and game theory

The first course of every track is free: SQL Fundamentals Interview Questions, Python Warm-Up for DSA, and Welcome to the Arena.

60 CODING PROBLEMS YOU SOLVE IN PYTHON
• A built-in code editor: write your solution, run it and get it checked
• 20 easy, 20 medium and 20 hard coding challenges, from Two Sum, Valid Parentheses and Binary Search to Merge Intervals, Coin Change, Trapping Rain Water, Edit Distance and Word Break
• Grouped by pattern: arrays and hashing, strings, two pointers, sliding window, matrix, dynamic programming, greedy and backtracking

20 GUIDED PATTERN PROJECTS
• Build one pattern step by step: two pointers, hash maps, sliding window, binary search, stack, BFS on a grid, tree DFS, heap top-k, intervals, tries, prefix sums, graph algorithms and more
• At every step you pick the right code block and see why it works

PRACTICE BETWEEN SESSIONS
• 50 interview questions and answers as flip cards: think first, then reveal the answer
• 50 quiz questions and review sessions to turn "I read it" into "I remember it"
• A cheat sheet with 67 entries on data structures, algorithms and SQL
• Save questions, keep notes on any lesson, and build streaks and XP
• An AI mentor that explains a concept in plain language when it refuses to click

WHO IT IS FOR
• Students preparing for a first internship or graduate role
• Developers getting ready for a technical interview
• Data analysts and engineers who expect SQL questions in a hiring loop
• Anyone who wants to learn algorithms properly, not just memorize answers

Lessons are short enough for a commute. The app is available in 22 languages.

FREE AND PRO
Free: the first course of each track, two coding problems, one guided project, the question cards, the quiz, the cheat sheet and three AI mentor questions a day.
Pro unlocks all 90 courses, all 60 coding problems, all 20 guided projects, course certificates and unlimited AI mentor answers. Subscriptions renew automatically and can be cancelled at any time in Google Play.

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