Array

vector<int> Solution::repeatedNumber(const vector<int> &A) {
    vector<int> copy(A.size()+1, 0);
    copy[0] = 1;
    vector<int> ans;
    for(int i = 0; i < A.size(); i++){
        copy[A[i]]++;
        if(copy[A[i]] > 1)
            ans.push_back(A[i]);
    }

    auto itr = find(copy.begin(), copy.end(), 0);
    ans.push_back(itr - copy.begin());
    return(ans);
}