Kth Missing Positive Number
Problem Statement - link #
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.
Examples #
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 <= n <= 10001 <= arr[i] <= 10001 <= k <= 1000arr[i] < arr[j]for1 <= i < j <= arr.length
Solutions #
class Solution {
public int findKthPositive(int[] arr, int k) {
int n = arr.length;
int left = 0, right = n-1;
while (left <= right) {
int mid = left + (right - left) / 2;
if (arr[mid] - mid - 1 < k) {
left = mid + 1;
} else {
right = mid - 1;
}
}
return left + k;
}
}