動機

猜數字

Problem

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 = 5Output: 9Explanation: 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 = 2Output: 6Explanation: 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?

sol

class Solution:
    def findKthPositive(self, arr: List[int], k: int) -> int:
        a, b = 0, max(arr[-1], len(arr)+k)
        while a<b:
            mid = (a+b)//2
            if mid-bisect_right(arr,mid) >= k:
                b = mid
            else:
                a = mid+1
        return a