Math & number theory
AlgorithmsGCD, primes, modular arithmetic, digit work — and watching for overflow / float precision.
Definition
Interview math leans on a few reusable tools: GCD/LCM via Euclid's algorithm, prime testing and the Sieve of Eratosthenes, modular arithmetic, and digit manipulation. JavaScript numbers are 64-bit floats — exact only up to 2⁵³ — so large-integer work needs BigInt.
When to use
Reach for these when a problem is about divisibility, primes, digits, powers, or combinatorics. The recurring traps are integer overflow and floating-point precision — prefer integer math and modular reduction over floats where you can.