Coin Change 2 LeetCode solution in Python

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class Solution:
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    def change(self, amount: int, coins: List[int]) -> int:
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        leng = len(coins)
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        def dfs(amount, start):
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            if amount == 0:
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                return 1
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            elif amount < 0:
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                return 0
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            res = 0
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            for i in range(start, leng):
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                res += dfs(amount - coins[i], i)
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            return res
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        return dfs(amount, 0)