K-th Smallest in Lexicographical Order LeetCode solution in Python

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class Solution:
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    def findKthNumber(self, n: int, k: int) -> int:
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        def prefix(op, n):
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            if op == n:
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                return 1
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            if int(op) > int(n):
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                return 0
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            for i in range(len(op)):
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                if int(op[i]) > int(n[i]):
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                    rem = len(n) - 1 - len(op)
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                    if not rem:
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                        return 1
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                    return 1 + int(10 * ((1 - 10**rem) / -9))
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                elif int(op[i]) < int(n[i]):
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                    rem = len(n) - len(op)
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                    if not rem:
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                        return 1
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                    return 1 + int(10 * ((1 - 10**rem) / -9))
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            res = 1
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            for i in range(10):
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                res += prefix(op + str(i), n)
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            return res
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        ans = 1
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        while k > 1:
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            pref = prefix(str(ans), str(n))
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            if pref >= k:
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                ans *= 10
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                k -= 1
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            else:
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                ans += 1
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                k -= pref
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        return ans