1492. The kth Factor of n

Description

Given two positive integers n and k.

A factor of an integer n is defined as an integer i where n % i == 0.

Consider a list of all factors of n sorted in ascending order, return the kth factor in this list or return -1 if n has less than k factors.

Constraints

• 1 <= k <= n <= 1000

Approach

Links

• Binarysearch

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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].

Solutions

Solution 1

/**
 * Time complexity : O(n)
 * Space complexity : O(1)
 */

class Solution {
    public int kthFactor(int n, int k) {
        for(int i = 1; i <= n/2; i++) {
            if(n % i == 0) {
                k--;
            }
            if(k == 0) {
                return i;
            }
        }
        return k == 1? n: -1;
    }
}

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