1207. Unique Number of Occurrences

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.

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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.

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Example 2:

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

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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

Solution

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class Solution {
    public boolean uniqueOccurrences(int[] arr) {
        int[] freq = new int[2001];
        
        for (int i = 0; i < arr.length; i++) {
            freq[arr[i] + 1000]++;
        }
        Set<Integer> set = new HashSet<>();
        for (int i = 0; i < freq.length; i++) {
            if (freq[i] > 0) {
               boolean prev = set.add(freq[i]);
                if (!prev) {
                    return false;
                }
            }        }
        return true;
    }
}

Solution#

Solution