README_EN.md

1539. Kth Missing Positive Number

中文文档

Description

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

Solutions

Python3

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) // 2
            if arr[mid] - mid - 1 < k:
                left = mid + 1
            else:
                right = mid
        return k - (arr[left - 1] - (left - 1) - 1) + arr[left - 1]

Java

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;
            int cur = mid == arr.length ? Integer.MAX_VALUE : arr[mid];
            if (cur - mid - 1 < k) {
                left = mid + 1;
            } else {
                right = mid;
            }
        }
        return k - (arr[left - 1] - (left - 1) - 1) + arr[left - 1];
    }
}

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