// integer to roman numeral
const intToRoman = function(num) {
    const rosettaStone = {
        1: 'I',
        5: 'V',
        10: 'X',
        50: 'L',
        100: 'C',
        500: 'D',
        1000: 'M'
    };            
    let resStr = '';

    for (let i = 1000; i >= 1; i /= 10) {
        const times = Math.trunc(num / i);
        if (times > 0) {
            if (times % 9 == 0) {
                resStr += rosettaStone[i]
                    .concat(rosettaStone[(times + 1) * i])    
            } else if (times % 8 == 0) {
                resStr += rosettaStone[(times - 3) * i]
                    .concat(rosettaStone[(times - 7) * i]
                    .repeat(3))
            } else if (times % 7 == 0) {
                resStr += rosettaStone[(times - 2) * i]
                    .concat(rosettaStone[(times - 6) * i]
                    .repeat(2))                
            } else if (times % 6 == 0) {
                resStr += rosettaStone[(times - 1) * i]
                    .concat(rosettaStone[i])
            } else if (times % 5 == 0) {
                resStr += rosettaStone[(times) * i] 
            } else if (times % 4 == 0) {
                resStr += rosettaStone[i]
                    .concat(rosettaStone[(times + 1) * i])   
            } else if (times <= 3) {
                resStr += rosettaStone[i].repeat(times);            
            } 
            num -= times * i;
        } 
    }        

    return resStr;            
};

// roman numeral to integer
const romanToInt = function(s) {
    const rosettaStone = {
        'I': 1,
        'V': 5,
        'X': 10,
        'L': 50,
        'C': 100,
        'D': 500,
        'M': 1000        
    };
    let result = 0;
    let lastValue = 0;

    for (let i = s.length -1; i >= 0; i--) {
        const value = rosettaStone[s[i]];
        if (lastValue > value) {
            result -= value;
        } else {
            result += value;
        }
        lastValue = value;
    }

    return result;
};