homework/codewars/6__Persistent_Bugger.js

// Write a function, persistence, that takes in a positive parameter num and returns its multiplicative persistence, which is the number of times you must multiply the digits in num until you reach a single digit.

// For example:

//  persistence(39) === 3 // because 3*9 = 27, 2*7 = 14, 1*4=4
//                        // and 4 has only one digit

//  persistence(999) === 4 // because 9*9*9 = 729, 7*2*9 = 126,
//                         // 1*2*6 = 12, and finally 1*2 = 2

//  persistence(4) === 0 // because 4 is already a one-digit number

function persistence(num) {
    let count = 0;
    function mult(n1) {
        if (n1 < 10) return 0;
        count++;
        mult(
            n1
                .toString()
                .split("")
                .map((x) => +x)
                .reduce((a, b) => a * b, 1)
        );
        return count;
    }
    return mult(num);
}