iskaprekar/index.js

Is the integer a Kaprekar number

function isKaprekar(num) {
    if(num < 1) {
        return false;
    } else if(num === 1) {
        return true;
    }

    // First we split the squared integer into an array of digits
    var num2   = num * num;
    var digits = splitNumber(num2);
    // Then we split the array into two and combine the digits back into integers
    for(var i = 0; i < digits.length; i++) {
        if(digits.length > 1) {
            var first  = combineNumber(digits.slice(0, i));
            var second = combineNumber(digits.slice(i));
        } else {
            var first = digits[0];
            var second = 0;
        }
        // Then we compare if the sum of these integers is the value the function got called with
        if((first + second) === num) {
            return true;
        }
    }
    return false;
}

function splitNumber(num) {
    var res = ('' + num).split('').map(function(item) {
        return parseInt(item, 10);
    });
    return res;
}

function combineNumber(arr) {
    return parseInt(arr.join(''));
}

console.log(isKaprekar(2));

module.exports = isKaprekar;
module.exports.splitNumber = splitNumber;
module.exports.combineNumber = combineNumber;