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63 lines
1.5 KiB
Markdown
63 lines
1.5 KiB
Markdown
# [1539. Kth Missing Positive Number](https://leetcode.com/problems/kth-missing-positive-number/)
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## 题目
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Given an array `arr` of positive integers sorted in a **strictly increasing order**, and an integer `k`.
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*Find the* `kth` *positive integer that is missing from this array.*
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**Example 1:**
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```
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Input: arr = [2,3,4,7,11], k = 5
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Output: 9
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Explanation: The missing positive integers are [1,5,6,8,9,10,12,13,...]. The 5th missing positive integer is 9.
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```
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**Example 2:**
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```
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Input: arr = [1,2,3,4], k = 2
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Output: 6
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Explanation: The missing positive integers are [5,6,7,...]. The 2nd missing positive integer is 6.
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```
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**Constraints:**
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- `1 <= arr.length <= 1000`
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- `1 <= arr[i] <= 1000`
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- `1 <= k <= 1000`
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- `arr[i] < arr[j]` for `1 <= i < j <= arr.length`
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## 题目大意
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给你一个 **严格升序排列** 的正整数数组 `arr` 和一个整数 `k` 。请你找到这个数组里第 `k` 个缺失的正整数。
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## 解题思路
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- 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 。
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## 代码
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```go
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package leetcode
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func findKthPositive(arr []int, k int) int {
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positive, index := 1, 0
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for index < len(arr) {
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if arr[index] != positive {
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k--
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} else {
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index++
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}
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if k == 0 {
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break
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}
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positive++
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}
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if k != 0 {
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positive += k - 1
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}
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return positive
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}
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``` |