Persistent Bugger.
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
reply
function persistence(num) {
return count(num,0);
function count(num,sum){
return (String(num).length>1)?count(String(num).split('').reduce((s,x)=>{return s=s*x},1),++sum):sum;
}
}
