JavaScript Practice 14/21

Smallest common multiple

The least common multiple (LCM) of two numbers is the smallest number both divide evenly into. There's a clean formula for it: lcm(a, b) = (a * b) / gcd(a, b), where gcd is the greatest common divisor - the biggest number that divides both evenly.

gcd itself has a short recursive definition: gcd(a, b) is a once b hits 0, and otherwise it's gcd(b, a % b). Once you have that one helper, finding the LCM of a whole range of numbers - not just two - is a loop: start with the smallest number as your running result, then fold in each next integer with the same two-number LCM formula.

Your task: write smallestCommonMultiple(arr), where arr is a two-number array like [1, 5] (in either order), returning the smallest number evenly divisible by every integer from the smaller to the larger, inclusive.

You'll practice:

Writing a short recursive helper function
Folding a two-argument formula over a range with a loop

// Write smallestCommonMultiple(arr): given a two-number array like [1, 5],
// return the smallest number evenly divisible by every integer in that
// range (inclusive), e.g. smallestCommonMultiple([1, 5]) === 60 (the LCM
// of 1, 2, 3, 4, and 5). The two numbers can arrive in either order.
function smallestCommonMultiple(arr) {

}