How LeetCode counts the number of occurrences of each number in an array

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0x01, Brief Description of Problem

Give you an array of integers arr, please help count the number of times each number appears in the array.

Returns true if the number of occurrences of each number is unique; otherwise returns false.

0x02, example

Example 1:

Input: arr = [1,2,2,1,1,3] Output: true Interpretation: In this array, 1 appears 3 times, 2 appears 2 times, and 3 appears only 1 time. No two numbers appear the same number of times. Example 2:

Input: arr = [1,2] Output: false Example 3:

Input: arr = [-3,0,1,-3,1,1,-3,10,0] Output: true

Tip:

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