LeetCode 268. Missing Number

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

Example 1
Input: [3,0,1]
Output: 2

Example 2
Input: [9,6,4,2,3,5,7,0,1]
Output: 8

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

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        for(int i=0; i<nums.size(); i++)
            if(nums[i]!=i)
               return i;
        return nums.size();
    }
};