leetcode之Find All Numbers Disappeared in an Array（448）

题目：

给定一个范围在 1 ≤ a[i] ≤ n ( n = 数组大小 ) 的整型数组，数组中的元素一些出现了两次，另一些只出现一次。

找到所有在 [1, n] 范围之间没有出现在数组中的数字。

您能在不使用额外空间且时间复杂度为O(n)的情况下完成这个任务吗? 你可以假定返回的数组不算在额外空间内。

示例:

输入:
[4,3,2,7,8,2,3,1]输出:
[5,6]

Python代码1：

思路：注意到数组元素个数跟元素范围是一样的，所以我们可以把出现过的元素对应下标位置的数字变成负数，最后把所有正数对应的下标拿出来，就是缺失的数字。

class Solution(object):def findDisappearedNumbers(self, nums):for i in range(len(nums)):index = abs(nums[i]) - 1nums[index] = -abs(nums[index])return [i + 1 for i in range(len(nums)) if nums[i] > 0]

python代码1升级版：

class Solution(object):def findDisappearedNumbers(self, nums):for n in nums:nums[abs(n) - 1] = -abs(nums[abs(n) - 1])return [i + 1 for i, n in enumerate(nums) if n > 0]

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