0448. Find All Numbers Disappeared in an Array.cpp

// 448.✅ Find All Numbers Disappeared in an Array

class Solution
{
public:
    vector<int> findDisappearedNumbers(vector<int> &nums)
    {
        vector<int> ans;
        set<int> s;

        for (int i = 0; i < nums.size(); ++i)
            s.insert(nums[i]);

        for (int i = 1; i <= nums.size(); ++i)
        {
            auto it = s.find(i);
            if (it == s.end())
                ans.push_back(i);
        }

        return ans;
    }
};