[592. Fraction Addition and Subtraction] #leetcode

592_1022.py

import re

class Solution(object):
    def fractionAddition(self, expression):
        """
        :type expression: str
        :rtype: str
        """
        signs = list()
        if expression[0] != "-":
            signs.append("+")
            
        signs.extend([c for c in expression if c in "+-"])
        
        prev_num = 0
        prev_den = 1
        i = 0
        
        for sub in re.split("(\\+)|(-)", expression):
            if sub and sub not in "-+":
                fraction = sub.split("/")
                num = int(fraction[0])
                den = int(fraction[1])
                g = abs(self.gcd(den, prev_den))
                if signs[i] == "+":
                    prev_num = prev_num * den / g + num * prev_den / g
                else:
                    prev_num = prev_num * den / g - num * prev_den / g
                i += 1
                
                prev_den = den * prev_den / g
                g = abs(self.gcd(prev_den, prev_num))
                prev_num /= g
                prev_den /= g
                
        
        return "{:d}/{:d}".format(int(prev_num), int(prev_den))
                
    @staticmethod
    def gcd(a, b):
        while b != 0:
            a, b = b, a % b
        return a