Given an unsorted array containing numbers and a number ‘k’, find the first ‘k’ missing positive numbers in the array.

Example 1:
Input: [3, -1, 4, 5, 5], k=3
Output: [1, 2, 6]
Explanation: The smallest missing positive numbers are 1, 2 and 6.

Example 2:
Input: [2, 3, 4], k=3
Output: [1, 5, 6]
Explanation: The smallest missing positive numbers are 1, 5 and 6.

Example 3:
Input: [-2, -3, 4], k=2
Output: [1, 2]
Explanation: The smallest missing positive numbers are 1 and 2.