DIY: Kth Missing Positive Number

Problem statement

You are given an array, a, of positive integers only and an integer, k. The array is sorted in a strictly increasing order. Your task is to find the kth positive integer that is missing from this array.

Constraints

• 1 <= a[i] <= 1000
• 1 <= k <= 1000
• a[i] <= a[j] for 1 <= i < j <= a.length

Input

The input will be an array of positive integers, sorted in ascending order, and an integer, k. The following are examples of the input to the function:

// Sample Input 1:
A = [1,2,3,4]
k = 2

// Sample Input 2:
A = [2,3,5,9,10]
k = 4

// Sample Input 3:
A = [1,97,101,654,798,989,1000]
k = 100

Output

The output will be an integer. Here are some examples of the output:

// Sample Output 1:
6

// Sample Output 2:
7

// Sample Output 3:
103