DataStructure_Algorithm_HandBook_PreForLeetCode

1207. Unique Number of Occurrences

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

solutions

So for the hash set,some of you might not very familiar with this structure.

Hash Set is a data structure implemented using a hash table, primarily used for quickly checking whether an element exists within a collection. It does not store duplicate elements, and the elements are typically unordered.

Hash Map is a data structure that stores data through keys, allowing for fast insertion, deletion, and retrieval of data. It employs a key-value pair mechanism to store data, where each key is unique.

The Set interface is part of the Java Collections Framework and represents a collection that does not allow duplicate elements. It is a more general collection type; HashSet, LinkedHashSet, and TreeSet are all implementations of this interface.

题目解析 首先使用哈希表来统计arr中每个数字的出现次数，然后再遍历记录过的出现次数，再次使用哈希表来进行判断是否重复出现即可。

Hash Set 是一种使用哈希表来实现的数据结构，主要用于快速地检查一个元素是否存在于集合中。它不存储重复的元素，而且通常元素是无序的。

Hash Map 是一种通过键来存储数据的数据结构，可以快速地插入、删除和获取数据。它使用键值对的方式来存储数据，其中键是唯一的。

Set 接口是 Java 集合框架中的一部分，代表了一种不允许重复元素的集合。它是一个更为通用的集合类型，HashSet、LinkedHashSet 和 TreeSet 都是这个接口的实现。