Formatted question description: https://leetcode.ca/all/1207.html

1207. Unique Number of Occurrences (Easy)

Given an array of integers arr, write a function that returns true if and only if the number of occurrences of each value in the array is unique.

 

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

Related Topics:
Hash Table

Solution 1.

// OJ: https://leetcode.com/problems/unique-number-of-occurrences/

// Time: O(N)
// Space: O(N)
class Solution {
public:
    bool uniqueOccurrences(vector<int>& A) {
        unordered_map<int, int> m;
        for (int n : A) m[n]++;
        unordered_set<int> s;
        for (auto &p : m) {
            if (s.count(p.second)) return false;
            s.insert(p.second);
        }
        return true;
    }
};

Java

class Solution {
    public boolean uniqueOccurrences(int[] arr) {
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        for (int num : arr) {
            int count = map.getOrDefault(num, 0);
            count++;
            map.put(num, count);
        }
        Set<Integer> set = new HashSet<Integer>();
        Set<Integer> keySet = map.keySet();
        for (int num : keySet) {
            int count = map.getOrDefault(num, 0);
            if (count != 0) {
                if (!set.add(count))
                    return false;
            }
        }
        return true;
    }
}

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