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class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        int n = nums.size();
        vector<bool> count(n + 1, false);
        for (int i = 0; i < n; i ++) {
            count[nums[i]] = true;
        }

        vector<int> res;
        for (int i = 1; i <= n; i ++) {
            if (!count[i]) {
                res.push_back(i);
            }
        }

        return res;
    }
};