Math

The O(n) Club: Fibonacci Number—Attack of the Useless Recursion ⚡ TL;DR If you’re asked for the nth Fibonacci number, please do not set your…

The O(n) Club: Power of Two — Bitwise Magic and the Ancient Single-Bit Prophecy ⚡ TL;DR Don’t know if your number is a power of two? Skip the…

The O(n) Club: Add Strings — When Java Says ‘No Cheating’, Do This ⚡ TL;DR Add two monster-sized numbers given as strings. You…

The O(n) Club: Cracking Integer Sqrt(x) Like a (Java) Boss ⚡ TL;DR Don’t use Math.sqrt(). Don’t dare touch floats. Compute the…

The O(n) Club: All Possible Parentheses — Recursion Goes Wild ⚡ TL;DR Given an expression like “2*3-4*5”, your job is to group…

The O(n) Club: Permutation Sequence — The Algorithmic VIP Pass ⚡ TL;DR Find the k-th permutation (in lex order) of numbers 1 to n… without…

The O(n) Club: Stack Your Sanity with LeetCode 224’s Basic Calculator ⚡ TL;DR Can you evaluate arithmetic strings with ‘+’,…

The O(n) Club: Exponentiation by Squaring in Java – Because Your CPU Has Feelings Too ⚡ TL;DR If you’re still looping through n…

The O(n) Club: When String Calculators Attack (a.k.a. LeetCode 227, but Funnier) ⚡ TL;DR Given a string with numbers and +, -, *, /, compute…

The O(n) Club: Multiply Strings Without Overflow (LeetCode 43 Edition) ⚡ TL;DR Stop trying to turn strings into integers—the numbers are too…