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448. Find All Numbers Disappeared in an Array

Difficulty Topics

Description

Given an array nums of n integers where nums[i] is in the range [1, n], return an array of all the integers in the range [1, n] that do not appear in nums.

 

Example 1:

Input: nums = [4,3,2,7,8,2,3,1]
Output: [5,6]

Example 2:

Input: nums = [1,1]
Output: [2]

 

Constraints:

  • n == nums.length
  • 1 <= n <= 105
  • 1 <= nums[i] <= n

 

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

Solution

find-all-numbers-disappeared-in-an-array.py
class Solution:
    def findDisappearedNumbers(self, nums: List[int]) -> List[int]:
        res = []

        for i, x in enumerate(nums):
            x = abs(x) - 1
            nums[x] = -abs(nums[x])

        for i, x in enumerate(nums):
            if x > 0:
                res.append(i + 1)

        return res