1060. Missing Element in Sorted Array

Given a sorted array A of unique numbers, find the K-th missing number starting from the leftmost number of the array.

Example 1:

Input: A = [4,7,9,10], K = 1
Output: 5
Explanation: 
The first missing number is 5.

Example 2:

Input: A = [4,7,9,10], K = 3
Output: 8
Explanation: 
The missing numbers are [5,6,8,...], hence the third missing number is 8.

Example 3:

Input: A = [1,2,4], K = 3
Output: 6
Explanation: 
The missing numbers are [3,5,6,7,...], hence the third missing number is 6.

Note:

1. 1 <= A.length <= 50000
2. 1 <= A[i] <= 1e7
3. 1 <= K <= 1e8