【leetcode】1539. Kth Missing Positive Number

题目如下：

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

解题思路：挨个比对就行了。

代码如下：

class Solution(object):
    def findKthPositive(self, arr, k):
        """
        :type arr: List[int]
        :type k: int
        :rtype: int
        """
        val = 1
        count = 0
        while len(arr) > 0:
            if val == arr[0]:
                arr.pop(0)
            else:
                count += 1
            if count == k:
                return val
            val += 1
        return val + (k - count - 1)