Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

For example,
Given nums = [0, 1, 3] return 2.

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

HashMap!

    public int missingNumber(int[] nums) 
    {
        Map<Integer,Integer> map = new HashMap<>();
        for(int i = 0; i < nums.length;i++)
        {
            map.put(nums[i],nums[i]);
        }
        
        int j;
        for(j=0;j<nums.length;j++)
        {
            if(!map.containsKey(j))
            break;
        }
        
        return j;
    }