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The Simplified 150Built to get you ready for any coding interview, campus drive to FAANG screen.
Grinding random problems is how most preparation fails. This is the ordered alternative: 150 problems in learning order, every one graded by real test cases, and every section sitting inside a lesson that derives its pattern by hand before you ever type.
Patterns, Big-O & the screening set
Cost analysis, the named shapes, and the bit tricks screeners open with.
- 1Classify the Complexityeasy
- 2Measure Space Usageeasy
- 3Name the Costeasy
- 4Power of Two, One Lineeasy
- 5Prime, Checked Properlyeasy
- 6Armstrong Numbereasy
- 7Second Largest, One Passeasy
- 8Reverse the Wordseasy
- 9Improve the Algorithmmedium
- 10Word Breakmedium
- 11Same Answer, Better Costmedium
- 12Product of Everything Elsemedium
- 13The Lonely Number (XOR)medium
- 14Count the 1 Bitsmedium
- 15The Missing Number, by XORmedium
- 16Rotate the Matrixmedium
- 17Three Sumhard
- 18Spiral Orderhard
Hashing
Have-I-seen-this-before, the single most used tool in interviews.
Two pointers
Sorted input plus a squeeze: O(n) answers where loops-in-loops read junior.
Sliding window
Best run obeying a rule, the shape behind half of all string questions.
- 1Average of Every Windoweasy
- 2Largest Sum of k in a Rowmedium
- 3Smallest Winning Windowmedium
- 4At Most K Different Lettersmedium
- 5Minimum Window Substringhard
- 6Longest Run Without Repeatshard
- 7Longest Ones After K Flipshard
- 8A Permutation Hides Insidehard
- 9Longest After K Repaintshard
- 10Maximum of Every Windowchallenge
Binary search
Halving, boundaries, and searching the answer space itself.
- 1Implement Binary Searcheasy
- 2Where Would It Goeasy
- 3Find First Occurrencemedium
- 4Square Root, Flooredmedium
- 5The First Yesmedium
- 6Search the Sorted Gridmedium
- 7Peak of the Mountainmedium
- 8Search in Rotated Arrayhard
- 9First Index of a Valuehard
- 10Koko Eats the Bananashard
- 11Smallest in the Rotated Listhard
- 12First and Last Positionhard
Sorting
The machinery: merge, partition, quickselect, and sorts used as tools.
- 1Bubble Sort That Knows When to Stopeasy
- 2Insertion Sorteasy
- 3Sort Colors (Dutch Flag)medium
- 4Merge Two Sorted Listsmedium
- 5Sort by a Second Valuemedium
- 6Partition Around a Pivotmedium
- 7The Missing Number, by Cyclic Sortmedium
- 8Count Inversionshard
- 9Merge Sort, the Whole Thinghard
- 10Quickselect the Kth Smallesthard
Linked lists
Fast and slow pointers, cycles and merges, the classic pointer discipline.
Stacks & queues
Most-recent-first and first-come-first-served, plus the monotonic stack.
Recursion
Self-similar problems, base cases, and trusting the smaller call.
Backtracking
Explore, prune, undo: every "all possible X" question lives here.
Trees & graphs
DFS, BFS, topological order: the heaviest-weighted interview topic.
- 1Maximum Deptheasy
- 2Count the Leaveseasy
- 3Validate BSTmedium
- 4Level Order Returnmedium
- 5Number of Islandsmedium
- 6Depth of a Nested Dictmedium
- 7Every Path Downmedium
- 8Can You Reach Itmedium
- 9The Widest Levelmedium
- 10Flood Fillmedium
- 11Course Schedule (Topological Sort)hard
- 12Shortest Hopshard
- 13A Safe Order to Take Courseshard
- 14Word Ladder Lengthhard
- 15Is It Actually a Treehard
Heaps & greedy
Top-k selection and provably-safe local choices.
Dynamic programming
Remembered subproblems, from Kadane to the knapsack.
- 1Climbing Stairseasy
- 2Cheapest Staircaseeasy
- 3House Robbermedium
- 4Best Day to Buy and Sellmedium
- 5Fewest Coinsmedium
- 6Unique Grid Pathsmedium
- 7Best Stretch (Kadane)medium
- 8Longest Common Subsequencehard
- 9Rob the Circlehard
- 10Decode Wayshard
- 11Longest Palindromic Substringhard
- 12Ways to Make Changehard
- 13Longest Increasing Subsequencehard
- 14The 0/1 Knapsackchallenge
150 problems. One order. Zero rupees.
Finish the climb and the timed rounds stop feeling like interviews and start feeling like reps. Sign up free and every solve is saved to your progress.