1207. Unique Number of Occurrences

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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

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