romanToInt.py

'''
Source : https://leetcode.com/problems/roman-to-integer/description/
Author : Yuan Wang
Date   : 2019-01-11

/********************************************************************************** 
*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, two is written as II in Roman numeral, just two one's added together.
*Twelve is written as, XII, which is simply X + II. The number twenty seven 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. Input is guaranteed to be within 
*the range from 1 to 3999.
**********************************************************************************/
'''

d = {'M':1000, 'D':500, 'C':100, 'L':50, 'X':10, 'V':5, 'I':1}

def romanToInt(s):
    res, p = 0, 'I'
    for c in s[::-1]:
        res, p = res - d[c] if d[c] < d[p] else res + d[c], c
    return res

import unittest
class Test(unittest.TestCase):

    def setUp(self):
        self.A = "III"
        self.B = "MCMXCIV"

    def test(self):
    	self.assertEqual(romanToInt(self.A),3)
    	self.assertEqual(romanToInt(self.B),1994)

if __name__ == '__main__':
    unittest.main()