Largest Multiple of Three LeetCode solution in Python

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class Solution:
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    def largestMultipleOfThree(self, digits: List[int]) -> str:
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        A = digits
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        A.sort()
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        A.reverse()
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        @cache
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        def DP(
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            i, r
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        ):  # max number whose remainder is r using subarray [0:i] (inclusive)
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            if i == 0:
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                if A[0] % 3 == r:
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                    return A[0]
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                else:
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                    return 0
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            Ra = DP(i - 1, r)
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            Rb = [
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                x for j in range(3) for x in (DP(i - 1, j) * 10 + A[i],) if x % 3 == r
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            ]
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            return max([Ra, *Rb])
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        ans = DP(len(A) - 1, 0)
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        if ans == 0 and 0 not in A:
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            return ""
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        else:
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            return str(ans)