448. Find All Numbers Disappeared in an Array -- Python_python given an array of integers where 1 ≤ a[i] ≤-优快云博客

本文探讨了一个有趣的问题：在一个包含重复元素的整数数组中找出所有不在数组中的[1,n]范围内的数字。提供了两种解决方案，一种是个人实现但效率较低的方法，另一种是在讨论区找到的高效解答。

448. Find All Numbers Disappeared in an Array

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]

code:
自己提交的（未被接受）：

class Solution:
    def findDisappearedNumbers(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        L = []
        if len(nums)==0:
            return L
        else:
            max_num=max(max(nums),len(nums))
            # for i in range(1,max_num+1):
            #     if i not in nums:
            #         L.append(i)
            L=[i for i in range(1,max_num+1) if i not in nums]
            return L

Discuss区的一个优秀答案：

class Solution:
    def findDisappearedNumbers(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        return list(set(range(1, len(nums) + 1)).difference(set(nums)))

此题用了自己的思路虽然可以做出来，但是效率太差了，这个是别人的参考答案。一个将近20000长度的list运行速度0.003秒，而我自己的代码运行时间3.7s，一直显示超时不被接受！ T T 差距啊！！