Number of Ways to Divide a Long Corridor LeetCode solution in Python

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class Solution:
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    def numberOfWays(self, corridor):
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        seat, res, plant = 0, 1, 0
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        for i in corridor:
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            if i == "S":
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                seat += 1
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            else:
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                if seat == 2:
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                    plant += 1
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            if seat == 3:
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                res = res * (plant + 1) % (10**9 + 7)
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                seat, plant = 1, 0
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        if seat != 2:
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            return 0
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        return res