# Solving Leetcode Interviews in Seconds with AI: Kth Missing Positive Number


	# Introduction
	In this blog post, we will explore how to solve the LeetCode problem "1539" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like [Chatmagic](https://www.chatmagic.app), we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

	# Problem Statement
	> Given an array arr of positive integers sorted in a strictly increasing order, and an integer k. Return the kth positive integer that is missing from this array.   Example 1:  Input: arr = [2,3,4,7,11], k = 5 Output: 9 Explanation: The missing positive integers are [1,5,6,8,9,10,12,13,...]. The 5th missing positive integer is 9.  Example 2:  Input: arr = [1,2,3,4], k = 2 Output: 6 Explanation: The missing positive integers are [5,6,7,...]. The 2nd missing positive integer is 6.    Constraints:  1 <= arr.length <= 1000 1 <= arr[i] <= 1000 1 <= k <= 1000 arr[i] < arr[j] for 1 <= i < j <= arr.length    Follow up: Could you solve this problem in less than O(n) complexity? 

	# Explanation
	Here's the breakdown of the solution:

*   **Binary Search:**  The core idea is to use binary search to efficiently find the position in the sorted array where the `k`th missing positive integer would be located.
*   **Count Missing Numbers:** For any index `mid` in the array, we can determine how many positive integers are missing *before* `arr[mid]` by calculating `arr[mid] - (mid + 1)`.
*   **Adjust Search Range:**  Based on whether the number of missing integers before `arr[mid]` is less than or greater than `k`, we adjust the search range (left/right pointers) accordingly.

*   **Runtime Complexity:** O(log n), where n is the length of the input array.
*   **Storage Complexity:** O(1)

	
	# Code
	```python
	def findKthPositive(arr, k):
    """
    Finds the kth positive integer that is missing from a sorted array.

    Args:
    arr (list): A list of positive integers sorted in strictly increasing order.
    k (int): The index of the missing positive integer to find.

    Returns:
    int: The kth missing positive integer.
    """
    left, right = 0, len(arr) - 1

    while left <= right:
        mid = (left + right) // 2
        missing = arr[mid] - (mid + 1)

        if missing < k:
            left = mid + 1
        else:
            right = mid - 1

    return left + k
	```