public static List<Integer> missingNumbers(List<Integer> arr, List<Integer> brr) {
    Map<Integer,Long> map1 = arr.stream().collect(Collectors.groupingBy(Function.identity(),TreeMap::new,Collectors.counting()));
    
    Map<Integer,Long> map2 = brr.stream().collect(Collectors.groupingBy(Function.identity(),TreeMap::new,Collectors.counting()));
    
    List<Integer> answer = new ArrayList<>();
    for(Integer key : map2.keySet()){
        if(map1.containsKey(key)){
            if(map1.get(key) < map2.get(key)){
                answer.add(key);
            }
        }
        else{
            answer.add(key);
        }
    }
    return answer;
    }
}

vector<int> missingNumbers(vector<int> arr, vector<int> brr) {
    int mn = *min_element(brr.begin(), brr.end());
    int mx = *max_element(brr.begin(), brr.end());
    vector<int> freq(mx - mn + 1, 0);
    for (int x : brr) freq[x - mn]++;
    for (int x : arr) freq[x - mn]--;
    vector<int> ans;
    for (int i = 0; i < freq.size(); i++)
        if (freq[i] != 0)
            ans.push_back(i + mn);

    return ans;
}

function missingNumbers(arr, brr) {
    
    const groupA = arr.reduce((acc, n) => {
        acc[n] = (acc[n] || 0) + 1;
        return acc;
    }, {});
    
    const groupB = brr.reduce((acc, n) => {
        acc[n] = (acc[n] || 0) + 1;
        return acc;
    }, {});
    
    var missing = [];
    for(const nu of brr){
        if(groupA[nu] !== groupB[nu] && missing.indexOf(nu) < 0){
            missing.push(nu);
        }
    }
   
    return missing.sort(function(a, b) {
        return a - b;
    });
}