乘法持久性,persistence

persistence.js

exports.splitMultiply = splitMultiply;
exports.persistence = persistence;

/**
 * 返回整数的乘法持久性.
 For example:
 because 3*9 = 27, 2*7 = 14, 1*4=4,and 4 has only one digit
 persistence(39) === 3;
 because 9*9*9 = 729, 7*2*9 = 126, 1*2*6 = 12, and finally 1*2 = 2
 persistence(999) === 4;
 because 4 is already a one-digit number
 persistence(4) === 0;

 * @param {Number} num 无符号正整形
 */
function persistence(num) {
    let n = 0;
    if(Number.isSafeInteger(num) && num > 0) {
        while ((num+'').length > 1)  {
           num =  splitMultiply(num);
           n++
        }
        return n;

    } else {
        throw new Error('input must be positive safe integer');
    }

}

/**
 * 将整数拆分,按位相乘,例如 123,拆为 1*2*3,返回结果 6
 * @param  {Number} num 无符号整数
 */
function splitMultiply(num) {
    let product = 1;

    for (let i of num.toString()) {
        product *= Number(i);
    }

    return product;
}

persistence.test.js

const {splitMultiply,persistence} = require('./persistence');

describe("persistence test",function() {
    it("persistence",function() {
        let testData = [
            {
                input:1,
                expect:0,
            },
            {
                input:34,
                expect:2,
            },
            {
                input:999,
                expect:4,
            }
        ]

        testData.forEach((ele) => {
            expect(persistence(ele.input)).toBe(ele.expect);
        })
    });
    it("splitMultiply",function() {
        let testData = [
            {
                input:1,
                expect:1,
            },
            {
                input:34,
                expect:12,
            },
            {
                input:999,
                expect:729,
            }
        ]

        testData.forEach((ele) => {
            expect(splitMultiply(ele.input)).toBe(ele.expect);
        })
    });
});