Find All Numbers Disappeared in an Array
Created: March 9, 2020 by [lek-tin]
Last updated: March 9, 2020
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]
Solution
class Solution:
def findDisappearedNumbers(self, nums: List[int]) -> List[int]:
N = len(nums)
result = []
for num in nums:
pos = abs(num) % N
if nums[pos] > 0:
nums[pos] = -nums[pos]
for i in range(1, N+1):
if nums[i%N] > 0:
result.append(i)
return result