Daily Coding Problem 216 -> roman numeral to decimal

problem_216.py

Given a number in Roman numeral format, convert it to decimal.

The values of Roman numerals are as follows:

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

In addition, note that the Roman numeral system uses subtractive notation for numbers such as IV and XL.

For the input XIV, for instance, you should return 14.


================================================Solution.py======================================================

def isSubtractionEntity(a,b):
	letters = ["I", "V", "X", "L", "C", "D", "M" ]
	#get the index of b
	b_i = -1
	a_i = -1
	for letter_i, letter in enumerate(letters):
		if letter == b:
			b_i = letter_i
		if letter ==a:
			a_i = letter_i

	if a_i == -1 or b_i == -1:
		raise Exception("letters doesn;t exist")
	if a_i < b_i:
		return True
	return False

def getValue(letter):
	values = {
		"I":1,
		"V":5,
		"X":10,
		"L":50,
		"C":100,
		"D":500,
		"M":1000
	}
	return values[letter]

def convertToNumeral(roman):
	romans = list(roman)
	i  = 0
	num = 0
	while i < len(romans)-1:
		if isSubtractionEntity(romans[i],romans[i+1]):
			num -= getValue(romans[i])
		else:
			num += getValue(romans[i])
		i += 1
	num += getValue(romans[-1])
	return num

romans_list = ["I","II","IV","V","VI","IX","X","XI","XX","XXI","XXIV","XXV","XL","L","LX","LXXIII","XC","C"]

for roman in romans_list:
	print("{}:{}".format(roman, convertToNumeral(roman)))


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