class Solution {
public:
    int missingNumber(vector<int>& nums) {
        if(nums.size()==1 && nums[0]==1)
        {
            return 0;
        }
        if(nums.size() == 1 && nums[0] == 0)
        {
            return 1;
        }
        int current_sum = 0;
        int max = INT_MIN;
        int min = INT_MAX;
        for(int i : nums)
        {
            current_sum = current_sum + i;
            if(max<i)
            {
                max = i;
            }
            if(min>i)
            {
                min = i;
            }
        }
        int expected_sum = 0;
        for(int i = 0; i<=max; i++)
        {
            expected_sum = expected_sum + i;
        }
        if(expected_sum - current_sum == 0)
        {
            if(min!=0)
            {
                return 0;
            }
            else
            {
                return max+1;
            }
        }
        return expected_sum - current_sum;

    }
};