Beautiful Array LeetCode solution in Python

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from itertools import permutations
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class Solution:
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    def invalid(self, x):
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        n = len(x)
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        flag = False
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        for i in range(n):
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            if flag:
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                break
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            for j in range(i + 2, n):
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                if flag:
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                    break
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                for k in range(i + 1, j):
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                    if 2 * x[k] == x[i] + x[j]:
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                        flag = True
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                        break
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        return flag
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    def beautifulArray(self, n: int) -> List[int]:
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        for perm in permutations(range(1, n + 1)):
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            if not self.invalid(perm):
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                return perm