hackerrank_extra-long-factorials.js

function processData(input) {
    var n = parseInt(input);
    
    var number = numberToArray(n);
    
    while(n > 1){
        number = multiplyArray(number, numberToArray(n-1));
        n--;
    }
    
    process.stdout.write(number.reverse().join(''));
}

var numberToArray = function(num){
    num += "";
    
    var digits = [];
    
    for(var i=0; i < num.length; i++){
        digits.push(parseInt(num[i]));
    }

    return digits.reverse();
};

var multiplyArray = function(arr1, arr2){
    
    //process.stdout.write(arr1.join('') + "\n\n");
    //process.stdout.write(arr2.join('') + "\n\n");
    //process.stdout.write("------ \n\n");
    
    var result = [];
    
    for (i = 0; i < arr1.length; ++i) {
        for (retenue = 0, j = 0; j < arr2.length || retenue > 0; ++j) {
            result[i + j] = (retenue += (result[i + j] || 0) + arr1[i] * (arr2[j] || 0)) % 10;
            retenue = Math.floor(retenue / 10);
        }
    }
    
    //process.stdout.write("RESULT: " + result.join('') + "\n\n");
    //process.stdout.write("------ \n\n");
    
    return result;
};

process.stdin.resume();
process.stdin.setEncoding("ascii");
_input = "";
process.stdin.on("data", function (input) {
    _input += input;
});

process.stdin.on("end", function () {
   processData(_input);
});