1207. Unique Number of Occurrences

Simple question

class Solution {
public:
    bool uniqueOccurrences(vector<int>& arr) {
        // count accurance
        map<int, int> cnt;
        for(int i=0;i<arr.size();i++){
            if (cnt.find(arr[i])==cnt.end()){
                cnt[arr[i]] = 1;
            }
            else{
                cnt[arr[i]] ++;
            }
        }
        
        // occurance time, unique
        set<int> aa;
        for(auto it = cnt.begin();it!=cnt.end();it++){
            aa.insert(it->second);
        }
        if (aa.size()==cnt.size()){
            return true;
        }
        else{
            return false;
        }
    }
};