Count Number of Special Subsequences LeetCode solution in Python

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# Runtime: 4322 ms (Top 46.43%) | Memory: 18 MB (Top 47.62%)
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class Solution:
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    def countSpecialSubsequences(self, nums: List[int]) -> int:
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        if not nums:
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            return 0
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        last_0 = 0
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        last_1 = 0
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        last_2 = 0
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        for i in nums:
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            if i == 0:
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                last_0 = (2 * last_0 + 1) % 1000000007
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            elif i == 1:
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                last_1 = (last_0 + 2 * last_1) % 1000000007
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            elif i == 2:
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                last_2 = (last_1 + 2 * last_2) % 1000000007
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        return last_2 % 1000000007