268 Missing Number

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

Example 1:

Input: nums = [3,0,1]
Output: 2
Explanation: n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.

Example 2:

Input: nums = [0,1]
Output: 2
Explanation: n = 2 since there are 2 numbers, so all numbers are in the range [0,2]. 2 is the missing number in the range since it does not appear in nums.

Example 3:

Input: nums = [9,6,4,2,3,5,7,0,1]
Output: 8
Explanation: n = 9 since there are 9 numbers, so all numbers are in the range [0,9]. 8 is the missing number in the range since it does not appear in nums.

Solution:

class Solution {
    public int missingNumber(int[] nums) {
        // base case 
        if (nums == null || nums.length == 0){
             return -1;
        }

        Set<Integer> set = new HashSet<Integer>();
        for (int i = 0; i < nums.length; i++){
            set.add(nums[i]);
        }

        int result = nums.length;

        for (int i = 0; i < nums.length; i++){
            if (!set.contains(i)){
                result = i;
                break;
            }
        }
        return result;
    }
}


// TC: O(n)
// SC: O(n)