1207. Unique Number of Occurrences
给予一个整数阵列，若该整数的每个数字出现次数都不重复返回true，否则false。
Example:
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.
Input: arr = [1,2]
Output: false
思路：
1.用HashMap统计每个数字的出现次数
2.用Set检查出现次数是否重复
JavaCode：