w07d5-solution.md

Assessment

Week 7 | Day 5

• In mathematics, the persistence of a number is the number of times one must apply a given operation to an integer before reaching a fixed point at which the operation no longer alters the number.
• The multiplicative persistence of 39 is 3, because it takes three steps to reduce 39 to a single digit: 39 → 27 → 14 → 4.
• Write a function to find the multiplicative persistence of a number. You must use recursion.

// Write a function to find the multiplicative persistence of a number. You must use recursion.

function multiply(numStr) {
    var total = 1;

    for (var i = 0; i < numStr.length; i++) {
        total = total * Number(numStr[i]);
    }

    return total;
}

function multiplicativePersistenceWithTimes(num, times) {
    var numStr = String(num);
    var newNum;

    if (num <= 9) {
        return times;
    }

    newNum = multiply(numStr); // 27
    return multiplicativePersistenceWithTimes(newNum, times + 1);
}

function multiplicativePersistence(num) {
    return multiplicativePersistenceWithTimes(num, 0)
}

multiplicativePersistence(39); //fn1
// multiplicativePersistence(27, 1); //fn2
// multiplicativePersistence(14, 2); //fn3
// multiplicativePersistence(4, 3);  //fn4
// // ---> 3

Have fun!