1539. Kth Missing Positive Number

Given an array arr of positive integers sorted in a strictly increasing order, and an integer k.

Find 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

class Solution {
    public int findKthPositive(int[] arr, int k) {
        int n = arr.length;
        int end = k + arr[n - 1];
        List<Integer> list = new ArrayList();
        
        for(int i : arr) list.add(i);
        int res = -1;
        for(int i = 1; i <= end; i++) {
            if(list.indexOf(i) < 0) k--;
            if(k == 0) {
                res = i;
                break;
            }
        }
        return res; 
    }
}