1207. Unique Number of Occurrences.cpp

/*
Given an array of integers arr, return true if the number of occurrences of each value in the array is unique, or false otherwise.

Example 1:
Input: arr = [1,2,2,1,1,3]
Output: true
Explanation: The value 1 has 3 occurrences, 2 has 2 and 3 has 1. No two values have the same number of occurrences.

Example 2:
Input: arr = [1,2]
Output: false

Example 3:
Input: arr = [-3,0,1,-3,1,1,1,-3,10,0]
Output: true
 
Constraints:
1 <= arr.length <= 1000
-1000 <= arr[i] <= 1000
*/ 

class Solution {
public:
    bool uniqueOccurrences(vector<int>& arr) {
        unordered_map<int, int> cnt;
        unordered_set<int> unq;
        for (int n : arr) 
            cnt[n]++;               
        for (auto& c : cnt) 
            unq.insert(c.second);   
        return cnt.size() == unq.size();
    }
};