LeetCode in Kotlin

1539. Kth Missing Positive Number

Easy

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 5^th 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 2^nd 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

Solution

class Solution {
    fun findKthPositive(arr: IntArray, k: Int): Int {
        var missed = 0
        for (i in arr.indices) {
            if (i == 0) {
                missed += arr[0] - 1
                if (missed >= k) {
                    return k
                }
            } else {
                missed += arr[i] - arr[i - 1] - 1
                if (missed >= k) {
                    missed -= arr[i] - arr[i - 1] - 1
                    var result = arr[i - 1]
                    while (missed++ < k) {
                        result++
                    }
                    return result
                }
            }
        }
        var result = arr[arr.size - 1]
        while (missed++ < k) {
            result++
        }
        return result
    }
}

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