LeetCode 448 Find All Numbers Disappeared in an Array

最新推荐文章于 2025-09-12 17:31:31 发布

SimminonGarcia

最新推荐文章于 2025-09-12 17:31:31 发布

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CC 4.0 BY-SA版权

文章标签：数据结构与算法 runtime

原文链接：https://juejin.im/post/5a3779226fb9a045186ad580

本文介绍了一个算法问题：如何在一个整数数组中找出所有未出现的元素。数组中的数字范围为1到n，部分数字重复出现。文章提供了一个不使用额外空间且运行时间为O(n)的Swift实现方案。

题目

Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements of [1, n] inclusive that do not appear in this array.

Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.

Example:

Input:
[4,3,2,7,8,2,3,1]

Output:
[5,6]
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代码

func findDisappearedNumbers(_ nums: [Int]) -> [Int] {
    var tmp = nums;
    var arr: [Int] = []
    for i in 0..<tmp.count {
        let index = abs(tmp[i])  - 1
        if tmp[index] > 0 {
            tmp[index] *= -1
        }
    }
    for i in 0..<tmp.count {
        if tmp[i] > 0 {
            arr.append(i+1)
        }
    }
    return arr;
}
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