Average Waiting Time LeetCode solution in Python

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class Solution:
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    def averageWaitingTime(self, customers: List[List[int]]) -> float:
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        start = customers[0][0]
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        end = start + customers[0][1]
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        total_wait = end - start
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        for c in customers[1:]:
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            start = c[0]
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            if start <= end:
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                end += c[1]
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                total_wait = total_wait + end - start
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            else:
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                end = c[0] + c[1]
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                total_wait += c[1]
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        return total_wait / len(customers)