Data Structures & Algorithms
Start from complexity analysis and work up to graphs and dynamic programming. Built for coding rounds and technical interviews.
Written byRohan Sharma
Foundations
4 lessons- 6 min read
What Are Data Structures and Algorithms
Why the way you store data decides how fast your program runs, and how to start thinking about both.
- 12 min read
Time Complexity
Big O, Big Omega, Big Theta and the little-o cousins — every notation used to describe how an algorithm grows, with practice questions along the way.
- 9 min read
Space Complexity
Memory has a cost too, and the recursion stack counts even when you never allocate anything.
- 8 min read
Recursion Fundamentals
Define a base case, shrink the input, and trust the recursive call to do the rest.
Foundations Quiz
12 questions
Python Essentials
1 lessonArrays & Strings
4 lessons- 9 min read
Arrays and Strings
How arrays are laid out in memory, which operations are cheap, and the traversal patterns you will reuse everywhere.
- 8 min read
Two Pointers Technique
Solve array problems in linear time by walking two indices toward each other instead of using nested loops.
- 6 min read
Sliding Window Technique
Maintain a moving range over an array to answer subarray questions in a single pass.
- 8 min read
Kadane's Algorithm and Prefix Sum Tricks
Find the best contiguous subarray without checking every one, using a habit of thought you will reuse in dozens of problems.
Arrays & Strings Quiz
8 questions
Searching & Sorting
14 lessons- 5 min read
Linear Search
Check every item one by one. The simplest search there is, and sometimes the only one that works.
- 9 min read
Binary Search
Halve the search space every step to find an element in logarithmic time, and recognise the problems that hide a binary search inside them.
- 6 min read
Jump Search
Skip ahead in fixed steps, then walk back. A middle ground between linear and binary search.
- 6 min read
Interpolation Search
Guess where the value probably is instead of always splitting down the middle.
- 7 min read
Exponential & Fibonacci Search
Two ways to find a range first, then search inside it — useful when the array is huge or seeking is expensive.
- 5 min read
Bubble Sort
Repeatedly swap neighbours that are out of order until nothing moves.
- 5 min read
Selection Sort
Find the smallest item, put it first, repeat. Minimal swaps, but never fast.
- 6 min read
Insertion Sort
Build a sorted section one item at a time, exactly how you sort a hand of cards.
- 8 min read
Merge Sort
Split in half, sort each half, then zip them together. Guaranteed n log n, every time.
- 8 min read
Quick Sort
Pick a pivot, push smaller left and bigger right, then repeat on each side.
- 7 min read
Heap Sort
Turn the array into a heap, then repeatedly pull out the largest. O(n log n) guaranteed, with no extra memory.
- 6 min read
Counting Sort
Tally how many times each value appears, then rebuild the array. No comparisons at all.
- 7 min read
Radix Sort
Sort by the last digit, then the next, and so on. The order appears without a single comparison.
- 6 min read
Searching & Sorting Cheat Sheet
Every algorithm side by side, with a decision guide for picking the right one under pressure.
Searching & Sorting Quiz
24 questions
Hashing
2 lessons- 9 min read
Hash Maps and Sets
Trade memory for near-constant lookups, and learn the handful of patterns that solve a huge share of interview problems.
- 9 min read
How a Hash Map Actually Works Inside
Peek under the hood at hash functions, load factor and resizing, and see why the answer is still O(1) on average.
Hashing Quiz
8 questions
String Algorithms
4 lessons- 7 min read
String Pattern Matching, From Brute Force Up
Find a word inside a much bigger text, starting from the obvious approach and seeing exactly where it wastes time.
- 9 min read
Rolling Hash and the Rabin-Karp Algorithm
Turn a whole substring into one number, update that number in O(1) as the window slides, and compare numbers instead of characters.
- 10 min read
The KMP Algorithm
Never re-check a character you have already matched. One precomputed table turns pattern matching into a guaranteed O(n + m).
- 9 min read
Manacher's Algorithm for Palindromes
Find the longest palindromic substring in linear time, by reusing palindromes you have already discovered instead of checking each centre from scratch.
Strings Quiz
8 questions
Linked Lists
2 lessons- 10 min read
Linked Lists
Nodes connected by pointers, the techniques that make them tractable, and why the dummy head trick removes most edge cases.
- 9 min read
Doubly Linked Lists and the LRU Pattern
Add a backward pointer, get O(1) removal from anywhere, and meet the structure behind every LRU cache.
Linked Lists Quiz
8 questions
Stacks & Queues
2 lessons- 9 min read
Stacks and Queues
Two restricted structures whose limitations are exactly what make them useful for nesting, ordering and traversal.
- 8 min read
Monotonic Deque and Sliding Window Maximum
Track the maximum of a moving window in O(1) per step, using a deque that only ever shrinks in one direction.
Stacks & Queues Quiz
8 questions
Trees
1 lessonHeaps & Priority Queues
1 lessonGraphs
4 lessons- 12 min read
Graphs and Traversal
Represent networks of relationships, then explore them with depth-first and breadth-first search.
- 11 min read
Dijkstra & Shortest Paths
BFS finds the fewest edges. When edges have weights, you need something smarter.
- 12 min read
Union-Find & Topological Sort
Track connected groups in near-constant time, and order tasks so every prerequisite comes first.
- 10 min read
Minimum Spanning Trees: Prim's and Kruskal's
Connect every node as cheaply as possible, using two classic greedy strategies that arrive at the same answer from opposite directions.
Graphs Quiz
18 questions
Greedy & Backtracking
2 lessonsDynamic Programming
5 lessons- 13 min read
Dynamic Programming
Recognise overlapping subproblems, cache them, and turn exponential recursion into linear time.
- 9 min read
1D DP Patterns: House Robber and Friends
A family of problems where the decision at each step is small, but the pattern quietly powers half the DP questions you will ever see.
- 12 min read
Grid DP and the Knapsack Family
Move from a 1D line of decisions to a 2D table, and meet the single most reused DP shape in interviews.
- 9 min read
Longest Increasing Subsequence
One problem, two solutions — a clean O(n²) DP and a clever O(n log n) upgrade using binary search where you would least expect it.
- 11 min read
String DP: LCS, Edit Distance and Palindromes
Two strings, a 2D table, and the recurrence pattern that solves comparison, transformation and palindrome problems alike.
Dynamic Programming Quiz
13 questions
Bit Manipulation
1 lessonAdvanced Structures
4 lessons- 9 min read
Tries: Trees Built From Words
Store thousands of words in a tree that shares every common prefix, and get autocomplete almost for free.
- 11 min read
Segment Trees for Range Queries
Answer "what is the min, max or sum of this range?" and update a value, both in O(log n), on an array that keeps changing.
- 9 min read
Fenwick Trees (Binary Indexed Trees)
The same O(log n) range-sum-with-updates power as a segment tree, in about ten lines, once you learn one bit trick.
- 10 min read
Design Problems: Combining Structures on Purpose
The real skill interviews test with "design a ___" questions — picking two structures that cover each other's weaknesses.
Advanced Structures Quiz
10 questions
Assessments
16 quizzesFoundations Quiz
Foundations · 12 questions
Python Essentials Quiz
Python Essentials · 10 questions
Arrays & Strings Quiz
Arrays & Strings · 8 questions
Searching & Sorting Quiz
Searching & Sorting · 24 questions
Hashing Quiz
Hashing · 8 questions
Strings Quiz
String Algorithms · 8 questions
Linked Lists Quiz
Linked Lists · 8 questions
Stacks & Queues Quiz
Stacks & Queues · 8 questions
Trees Quiz
Trees · 6 questions
Heaps Quiz
Heaps & Priority Queues · 7 questions
Graphs Quiz
Graphs · 18 questions
Greedy & Backtracking Quiz
Greedy & Backtracking · 8 questions
Dynamic Programming Quiz
Dynamic Programming · 13 questions
Bit Manipulation Quiz
Bit Manipulation · 8 questions
Advanced Structures Quiz
Advanced Structures · 10 questions
DSA Final Assessment
Final assessment · 13 questions