Fraction Addition and Subtraction — LeetCode 592 Python Solution

The problem

Given a string expression representing an expression of fraction addition and subtraction, return the calculation result in string format. The final result should be an irreducible fraction.

Example

Input

expression = "-1/2+1/2"

Output

"0/1"

Python solution

class Solution:
    def fractionAddition(self, expression: str) -> str:
        x, y = 0, 6 * 7 * 8 * 9 * 10
        if expression[0].isdigit():
            expression = '+' + expression
        i, n = 0, len(expression)
        while i < n:
            sign = -1 if expression[i] == '-' else 1
            i += 1
            j = i
            while j < n and expression[j] not in '+-':
                j += 1
            s = expression[i:j]
            a, b = s.split('/')
            x += sign * int(a) * y // int(b)
            i = j
        z = gcd(x, y)
        x //= z
        y //= z
        return f'{x}/{y}'

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 592. Fraction Addition and Subtraction is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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