13.Roman_To_Integer.py

# Roma numerals are represented by seven different symbols.
# Symbol         Value
#   I       -       1
#   V       -       5
#   X       -       10
#   L       -       50
#   C       -       100
#   D       -       500
#   M       -       1000
# For examole, 2 is written as II in Roman numeral, just two ones 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.

# Give a roman numeral, convert it to an integer.
# Example 1:
# Input: s = "III"
# Output: 3
# Explanation : III = 3.

# Example 2:
# Input: s = "LVII"
# Output: 58
# Explanation: L = 50, V = 5, II = 3

# Example 3:
# Input: s = "MCMXCIV"
# Output: 1994
# Explanation: M = 1000, CM = 900, XC = 90 and IV = 4


# Solution:-

class Solution(object):
    def romanToInt(self, s):
        d = {'I':1, 'V':5, 'X':10, 'L':50, 'C':100, 'D':500, 'M':1000}
        sum = 0
        n = len(s)
        i = 0
        while i < n:
            if i < n-1 and d[s[i]] < d[s[i+1]]:
                sum += d[s[i+1]] - d[s[i]]
                i += 2
            else:
                sum += d[s[i]]
                i += 1

            return sum