1207.Unique_Number_of_Occurrences(Easy).md

1207. Unique Number of Occurrences (Easy)

Date and Time: Oct 21, 2024, 16:59 (EST)

Link: https://leetcode.com/problems/unique-number-of-occurrences/

Question:

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

Walk-through:

1. Convert arr into hashmap{}

2. Add all occurences into set(), for each occurence, check if it exists in set() already. If so, return False. Otherwise, return True in the end.

Python Solution:

class Solution:
    def uniqueOccurrences(self, arr: List[int]) -> bool:
        # For each elems in arr, know if occurrences are unique
        # Convert arr into a hashmap [elem: occurrences]
        # Append all the occruences into lst[], comapre with set(lst)
        
        # TC: O(n), SC: O(n)
        hashmap = Counter(arr)
        res = set()
        for val in hashmap.values():
            if val in res:
                return False
            else:
                res.add(val)

        return True

Time Complexity: $O(n)$, n is the length of arr.
Space Complexity: $O(n)$