LeetCode 1539. Kth Missing Positive Number Solution in Java, C++, Python & Go | Explanation + Code

Description

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?

Solutions

Solution 1

PythonJavaC++Go

class Solution: def findKthPositive(self, arr: List[int], k: int) -> int: if arr[0] > k: return k left, right = 0, len(arr) while left < right: mid = (left + right) >> 1 if arr[mid] - mid - 1 >= k: right = mid else: left = mid + 1 return arr[left - 1] + k - (arr[left - 1] - (left - 1) - 1)(code-box)

class Solution { public int findKthPositive(int[] arr, int k) { if (arr[0] > k) { return k; } int left = 0, right = arr.length; while (left < right) { int mid = (left + right) >> 1; if (arr[mid] - mid - 1 >= k) { right = mid; } else { left = mid + 1; } } return arr[left - 1] + k - (arr[left - 1] - (left - 1) - 1); } }(code-box)

class Solution { public: int findKthPositive(vector<int>& arr, int k) { if (arr[0] > k) return k; int left = 0, right = arr.size(); while (left < right) { int mid = (left + right) >> 1; if (arr[mid] - mid - 1 >= k) right = mid; else left = mid + 1; } return arr[left - 1] + k - (arr[left - 1] - (left - 1) - 1); } };(code-box)

func findKthPositive(arr []int, k int) int { if arr[0] > k { return k } left, right := 0, len(arr) for left < right { mid := (left + right) >> 1 if arr[mid]-mid-1 >= k { right = mid } else { left = mid + 1 } } return arr[left-1] + k - (arr[left-1] - (left - 1) - 1) }(code-box)