An Offerland course

Algorithms for Interviews

All the core techniques of algorithm interviews, from arrays to dynamic programming. Short lessons with diagrams, problems with automatic code checking, and explaining your solution out loud to an AI interviewer, just like in a real interview.

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Getting Started

How the course works and how to evaluate solutions: Big O made simple.

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How to Take This Course Complexity: Big O Made Simple Balance After Each Day Explain It in Your Own Words: Big O

Arrays and Two Pointers

When two pointers turn O(n²) into O(n).

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Two Pointers Mirror Phrase Check Squares in Order Pair in a Sorted List Zero-Sum Triples Explain It in Your Own Words: Two Pointers

Sliding Window and Prefix Sums

Subarrays and substrings without redundant recomputation.

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Sliding Window Best Window Average Shortest Stretch to the Goal Longest Repeat-Free Stretch Prefix Sums Stretches With an Exact Total Explain It in Your Own Words: Sliding Window

Hash Tables

O(1) lookup: the most common optimization in interviews.

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Hash Tables and Sets Does Any Value Repeat Pair With a Target Sum Note From Clipped Letters Anagram Buckets Longest Unbroken Run Explain It in Your Own Words: Hash Tables

Linked Lists

Pointers, the dummy head, and fast and slow pointers.

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Linked Lists Flip the Chain Midpoint of a List Zip Two Sorted Chains Adding Digit Lists Explain It in Your Own Words: Reversing a List

Stack and Queue

Brackets, "next greater," and the monotonic stack.

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Stack, Queue, and Monotonic Stack Bracket Balance Next Larger on the Right Waiting for a Higher Price Explain It in Your Own Words: Monotonic Stack

Trees

Depth-first and breadth-first traversals, recursion without fear.

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Binary Trees and Recursion Traversals: Depth-First and Breadth-First Tree Height Mirror the Tree Identical Trees Longest Path in a Tree Tree Rows by Depth Binary Search Tree (BST)Is It a Search Tree?Explain It in Your Own Words: DFS and BFS

Graphs

Grids, islands and dependency order.

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Graphs: Representation and Traversal Land Regions on a Map Largest Forest Patch Infection Spread Time Clusters of Linked Servers Topological Sort Module Build Order Explain It in Your Own Words: Topological Sort

Heap

Top-K and "the biggest one right now."

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Heaps and Priority Queues Boulder Crusher K-th Highest Score Most Common Values Explain It in Your Own Words: Heaps and Top-K

Binary Search

Not just in arrays: searching on the answer.

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Binary Search Find in a Sorted List Slot on a Sorted Shelf Minimum of a Shifted List Slowest Reading Pace Explain It in Your Own Words: Binary Search on the Answer

Backtracking

Subsets, permutations, and combinations.

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Backtracking Every Topping Combo All Orderings Weight Sets for an Exact Load Keypad Words Explain It in Your Own Words: Backtracking

Dynamic Programming

How to turn brute force into a table.

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DP: From Recursion to a Table Paving a Garden Path Cheapest Climb to the Top No Back-to-Back Shifts Fewest Bills 2D Dynamic Programming Counting Grid Routes Longest Shared Thread Explain It in Your Own Words: Dynamic Programming