LeetCodeMaththe kth factor of n

Posted 2020-12-14

题目：

给定两个正整数n和k。

整数n的因数定义为整数i，其中n％i == 0。

考虑按升序排列的所有n个因子的列表，返回此列表中的第k个因子；如果n小于k个因子，则返回-1。

Example 1:

Input: n = 12, k = 3
Output: 3
Explanation: Factors list is [1, 2, 3, 4, 6, 12], the 3rd factor is 3.

Example 2:

Input: n = 7, k = 2
Output: 7
Explanation: Factors list is [1, 7], the 2nd factor is 7.

Example 3:

Input: n = 4, k = 4
Output: -1
Explanation: Factors list is [1, 2, 4], there is only 3 factors. We should return -1.

Example 4:

Input: n = 1, k = 1
Output: 1
Explanation: Factors list is [1], the 1st factor is 1.

Example 5:

Input: n = 1000, k = 3
Output: 4
Explanation: Factors list is [1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000].

 

Constraints:

• 1 <= k <= n <= 1000

【解法】

待续