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

题意

在一个严格递增的正整数数组中找到第k个缺失的正整数。

思路

直接从1开始遍历找即可。

代码实现

Java

class Solution {
    public int findKthPositive(int[] arr, int k) {
        int ans = -1;
        int i = 0, j = 1;
        while (k != 0) {
            if (i < arr.length && j == arr[i]) {
                i++;
            } else {
                ans = j;
                k--;
            }
            j++;
        }
        return ans;
    }
}