Description
Given two integers n and k, return the kth lexicographically smallest integer in the range [1, n].
Example 1:
Input: n = 13, k = 2 Output: 10 Explanation: The lexicographical order is [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9], so the second smallest number is 10.
Example 2:
Input: n = 1, k = 1 Output: 1
Constraints:
1 <= k <= n <= 109
Solution
Python3
class Solution:
def findKthNumber(self, n: int, k: int) -> int:
def fn(x):
"""Return node counts in denary trie."""
ans, diff = 0, 1
while x <= n:
ans += min(n - x + 1, diff)
x *= 10
diff *= 10
return ans
x = 1
while k > 1:
cnt = fn(x)
if k > cnt: k -= cnt; x += 1
else: k -= 1; x *= 10
return x