English
1539. Kth Missing Positive Number
Problem Statement
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]
for1 <= i < j <= arr.length
Follow up:
Could you solve this problem in less than O(n) complexity?
Click to open Hints
- Keep track of how many positive numbers are missing as you scan the array.
Solution:
rs
impl Solution {
pub fn find_kth_positive(arr: Vec<i32>, k: i32) -> i32 {
let (mut l, mut r) = (0, arr.len());
while l < r {
let mid = l + (r - l) / 2;
if arr[mid] - mid as i32 - 1 >= k {
r = mid;
} else {
l = mid + 1;
}
}
l as i32 + k
}
}
...