Minimum Incompatibility LeetCode solution in Python

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class Solution(object):
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    def minimumIncompatibility(self, nums, k):
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        nums.sort(reverse=True)
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        upperbound = len(nums) // k
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        arr = [[] for _ in range(k)]
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        self.res = float("inf")
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        def assign(i):
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            if i == len(nums):
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                self.res = min(self.res, sum(arr[i][0] - arr[i][-1] for i in range(k)))
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                return True
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            flag = 0
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            for j in range(k):
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                if not arr[j] or (len(arr[j]) < upperbound and arr[j][-1] != nums[i]):
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                    arr[j].append(nums[i])
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                    if assign(i + 1):
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                        flag += 1
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                    arr[j].pop()
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                if flag >= 2:
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                    break
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            return flag != 0
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        if max(collections.Counter(nums).values()) > k:
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            return -1
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        assign(0)
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        return self.res