romantoInteger.js

//////////////////////////////////////////////Roman to Integer///////////////////////////////////////////////////////
// Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.
// Symbol       Value
// I             1
// V             5
// X             10
// L             50
// C             100
// D             500
// M             1000
// For example, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply
// X + II. The number 27 is written as XXVII, which is XX + V + II.
//
// Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII.
// Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same
// principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:
// I can be placed before V (5) and X (10) to make 4 and 9.
// X can be placed before L (50) and C (100) to make 40 and 90.
// C can be placed before D (500) and M (1000) to make 400 and 900.
// Given a roman numeral, convert it to an integer.
// Example 1:
//
// Input: s = "III"
// Output: 3
// Example 2:
//
// Input: s = "IV"
// Output: 4
// Example 3:
//
// Input: s = "IX"
// Output: 9
// Example 4:
//
// Input: s = "LVIII"
// Output: 58
// Explanation: L = 50, V= 5, III = 3.
// Example 5:
//
// Input: s = "MCMXCIV"
// Output: 1994
// Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
//
// Constraints:
// 1 <= s.length <= 15
// s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').
// It is guaranteed that s is a valid roman numeral in the range [1, 3999].
const romanToInt = function(s) {
    let str = s.split(''), res = 0;

    const romanToInt = {
        I: 1,
        V: 5,
        X: 10,
        L: 50,
        C: 100,
        D: 500,
        M: 1000
    };

    for (let i = 0; i < str.length; i++){
        if(romanToInt.hasOwnProperty(str[i])){
            if (i === 0) {
                res += romanToInt[str[i]];
            }else if(str[i - 1] === 'I' && str[i] === 'V'){
                res += (4 - 1);
            }else if(str[i - 1] === 'I' && str[i] === 'X'){
                res += (9 - 1);
            }else if(str[i - 1] === 'X' && str[i] === 'L'){
                res += (40 - 10);
            }else if(str[i - 1] === 'X' && str[i] === 'C'){
                res += (90 - 10);
            }else if(str[i - 1] === 'C' && str[i] === 'D'){
                res += (400 - 100);
            }else if(str[i - 1] === 'C' && str[i] === 'M'){
                res += (900 - 100);
            }else{
                res += romanToInt[str[i]];
            }
        }
    }

    return res;
};

// console.log(romanToInt("III"));
// console.log(romanToInt("IV"));
// console.log(romanToInt("IX"));
// console.log(romanToInt("LVIII"));
// console.log(romanToInt("MCMXCIV"));