Learn DSA

Patterns, practice and progress
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Learn to recognize the pattern

Learn the patterns behind interview problems, then practice them with auto-graded tests.

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Big-O and Reading Constraints

Unit 1 lesson, 13 min

Start the course

Work through 15 units in order, or jump to a pattern you want to practice. Each unit pairs runnable Python lessons with a problem ladder and a reference sheet. Basic Python knowledge helps; every unit is open.

Roadmap

Foundations

Complexity, hashing and the array patterns every interview starts with.

0/5 units
  1. Unit 1
    You are here

    Big-O & the Python Toolkit

    Read constraints like an interviewer, estimate Big-O at a glance, and know which Python built-ins hide an O(n) loop. Plus a step-by-step routine for attacking any problem.

    0/3 lessons, 0/7 problems
  2. Unit 2

    Arrays & Hashing

    Trade memory for speed: sets and dicts answer "have I seen this?" in O(1), turning nested loops into a single pass. Counting, grouping by a key, complement lookups and prefix passes.

    0/3 lessons, 0/9 problems
  3. Unit 3

    Two Pointers

    Walk two indices through an array instead of nesting loops: pointers from both ends for sorted pairs and palindromes, read/write pointers for in-place edits, and sort-then-squeeze for k-sum.

    0/3 lessons, 0/7 problems
  4. Unit 4

    Sliding Window

    Answer questions about contiguous subarrays and substrings in one pass: grow the window on the right, shrink it on the left, and never recompute from scratch.

    0/3 lessons, 0/7 problems
  5. Unit 5

    Prefix Sums

    Precompute running totals once, then answer any range sum in O(1). Pair them with a hash map to count subarrays, extend them to 2D grids, and run them in reverse as difference arrays.

    0/3 lessons, 0/7 problems

Core Patterns

Stacks, binary search, linked lists, trees, heaps and backtracking.

0/6 units
  1. Unit 6

    Stacks & Monotonic Stacks

    Last in, first out: match brackets, evaluate expressions, carry extra state, and use monotonic stacks to find the next greater or smaller element in O(n).

    0/3 lessons, 0/7 problems
  2. Unit 7

    Binary Search

    Halve the search space every step: one first-true template covers sorted arrays, lower/upper bounds, rotated arrays, matrices and "binary search on the answer".

    0/3 lessons, 0/7 problems
  3. Unit 8

    Linked Lists

    Rewire nodes instead of shifting elements: dummy heads, in-place reversal, fast & slow pointers, and merging, splitting and reordering chains.

    0/3 lessons, 0/8 problems
  4. Unit 9

    Trees: DFS & BFS

    Think recursively: each call answers a question about one subtree. Master DFS (pre/in/post-order), BFS level by level, and the BST property.

    0/3 lessons, 0/8 problems
  5. Unit 10

    Heaps & Top-K

    Always know the smallest (or largest) item in O(1) and update in O(log n). Heaps power top-k, k-way merge, running medians and schedulers.

    0/3 lessons, 0/7 problems
  6. Unit 11

    Backtracking

    Generate every subset, permutation or placement by making one choice at a time, exploring it, and undoing it. Prune dead branches early to keep exponential searches fast enough.

    0/3 lessons, 0/7 problems

Advanced

Graphs, dynamic programming, greedy, tries and bits.

0/4 units
  1. Unit 12

    Graphs

    Model anything with connections (maps, grids, dependencies, networks) as a graph, then explore it with DFS and BFS, order it with topological sort, group it with union–find and find cheapest routes with Dijkstra.

    0/3 lessons, 0/8 problems
  2. Unit 13

    Dynamic Programming

    Turn exponential recursion into fast code by solving each subproblem once. Learn the state, transition, base case, answer recipe, then apply it to 1D, grid, two-string and knapsack problems.

    0/3 lessons, 0/9 problems
  3. Unit 14

    Greedy & Intervals

    Make the locally best move and prove it never hurts: Kadane, reach-based jumping, and the sort-then-sweep toolkit for merging, scheduling and counting intervals.

    0/3 lessons, 0/8 problems
  4. Unit 15

    Tries & Bit Manipulation

    Prefix trees for autocomplete, wildcard and board word searches, plus the bit tricks (XOR, masks, x & (x - 1)) that turn tricky problems into one-liners.

    0/3 lessons, 0/8 problems

Activity

0 problems solved in the last 12 weeks