[Python手撕]字典序的第K小数字

class Solution:
    def findKthNumber(self, n: int, k: int) -> int:

        def findk(n,k):

            def countsteps(prefix,n):
                start = prefix
                end = prefix+1
                steps = 0

                while start <= n:
                    steps += min(n+1,end)-start
                    start *= 10
                    end *= 10
                
                return steps
            

            current = 1
            k -= 1

            while k > 0:
                steps = countsteps(current, n)
                if steps <= k:
                    current += 1
                    k -= steps
                elif steps > k:
                    current *= 10
                    k -= 1
            
            return current


        return findk(n,k)