268. Missing Number

Sort

class Solution {
public:
    int missingNumber(vector<int>& nums)
    {
        int n = nums.size();
        for(int i = 0; i < nums.size(); i++)
        {
            n += i - nums[i];
        }
        return n;
    }
};

• T: $O(n)$
• S: $O(1)$