leetcode-1207-easy

Unique Number of Occurences

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

思路一：用 map 统计

    public boolean uniqueOccurrences(int[] arr) {
        Map<Integer, Integer> map = new HashMap<>();

        for (int a : arr) {
            map.compute(a, (k, v) -> v == null ? 1 : v + 1);
        }

        Set<Integer> set = new HashSet<>(map.values());

        return set.size() == map.size();
    }