leetcode/lcci/17.04.Missing Number/Solution.cpp

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