Integer to Roman

https://leetcode.com/problems/integer-to-roman

自己写了一堆啰嗦的规则来选‘最适合’ 的数，结果全是bug。不如直接把数字按位数拆开，然后一一映射来得简洁。

var intToRoman = function(num) {
    var roman = [
    ['','M','MM','MMM'],
    ['','C','CC','CCC','CD','D','DC','DCC','DCCC','CM'],
    ['','X','XX','XXX','XL','L','LX','LXX','LXXX','XC'],
    ['','I','II','III','IV','V','VI','VII','VIII','IX']]

    var a = [parseInt(num / 1000) %10,
    parseInt(num / 100)%10,
    parseInt(num / 10)%10,
    num % 10];
    console.log(a);
    return a.map(function(n, i){
        return roman[i][n];
    }).join('');
}