leetcode 440 字典序的第k小数字

class (object):
    def findKthNumber(self, n, k):
        """
        :type n: int
        :type k: int
        :rtype: int
        """
        def getSteps(cur1, cur2, n):
            steps = 0
            while cur1 <= n:
                steps += min(n+1, cur2) - cur1
                cur1 *= 10
                cur2 *= 10
            return steps
            
        cur = 1
        k = k-1
        while k > 0:
            steps = getSteps(cur, cur+1, n)
            if k >= steps:
                cur = cur + 1
                k = k - steps
            else:
                cur = cur * 10
                k = k - 1
        return cur