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.

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 boolean uniqueOccurrences(int[] arr) {
          Arrays.sort(arr);
          HashMap<Integer, Integer> map = new HashMap();
          for(int i: arr){
              map.put(i, 1 + map.getOrDefault(i, 0));
          }
          ArrayList<Integer> list = new ArrayList(map.values());
          Collections.sort(list);
          for(int i = 1; i < list.size(); i++){
              if(list.get(i) == list.get(i-1)) return false;
          }
          return true;
      }
  }

  绕远路还是我会绕。

HashMap的values() 方法返回一个values的set，形式为collections，所以可以转化为list