1539. Kth Missing Positive Number

# 1539. Kth Missing Positive Number#

## 题目 #

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`

## 解题思路 #

• 简单题。用一个变量从 1 开始累加，依次比对数组中是否存在，不存在的话就把 k - -，直到 k 为 0 的时候即是要输出的值。特殊情况，missing positive 都在数组之外，如例子 2 。

## 代码 #

``````package leetcode

func findKthPositive(arr []int, k int) int {
positive, index := 1, 0
for index < len(arr) {
if arr[index] != positive {
k--
} else {
index++
}
if k == 0 {
break
}
positive++
}
if k != 0 {
positive += k - 1
}
return positive
}
``````

Apr 8, 2023