Fraction Addition and Subtraction LeetCode solution in Python

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# Runtime: 35 ms (Top 88.02%) | Memory: 14.1 MB (Top 5.79%)
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"""
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approach:
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first replace - with +- in the string so that implementation gets
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a little easy
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"""
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class Solution:
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    def fractionAddition(self, expression: str) -> str:
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        expression = expression.replace("-", "+-")
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        parts = [item for item in expression.split("+") if item != ""]
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        numes, denoms, denom_set, lcm = [], [], set(), 1
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        def get_lcm(a, b):
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            if a == 1:
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                return b
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            if b == 1:
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                return a
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            if a < b:
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                if b % a == 0:
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                    return a * get_lcm(1, b / a)
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                else:
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                    return a * get_lcm(1, b)
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            else:
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                if a % b == 0:
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                    return b * get_lcm(a / b, 1)
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                else:
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                    return b * get_lcm(a, 1)
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        for part in parts:
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            num, den = part.split("/")
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            numes.append(int(num))
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            denoms.append(int(den))
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            lcm = get_lcm(lcm, int(den))
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        result = 0
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        for num, den in zip(numes, denoms):
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            result += num * int(lcm / den)
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        def get_gcd(a, b):
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            if a == 0:
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                return b
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            if b == 0:
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                return a
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            if a == b:
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                return a
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            elif a < b:
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                return get_gcd(a, b - a)
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            else:
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                return get_gcd(a - b, b)
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        gcd = get_gcd(abs(result), lcm)
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        return str(int(result / gcd)) + "/" + str(int(lcm / gcd))