448. Find All Numbers Disappeared in an Array

Problem

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 <= 10^5

• 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 (Java)

class Solution {
    public List<Integer> findDisappearedNumbers(int[] nums) {
        int[] arr = new int[nums.length];
        int counter = 0;
        for (int i = 0; i < nums.length; i++) {
            arr[nums[counter] - 1] = 1;
            counter++;
        }
        List<Integer> res = new ArrayList<>();
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == 0) {
                res.add(i + 1);
            }
        }
        return res;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).