Unique Number of Occurrences
Easy · Arrays & Hashing · Array · Hash Table
Problem
Given an integer array arr, count how many times each distinct value occurs. Return true if no two distinct values occur the same number of times, and false otherwise.
Examples
Input: arr = [1, 2, 2, 1, 1, 3] Output: true
1 occurs 3 times, 2 twice and 3 once: three different counts.
Input: arr = [1, 2] Output: false
Both values occur once.
Input: arr = [-3, 0, 1, -3, 1, 1, 1, -3, 10, 0] Output: true
The counts are 3, 2, 4 and 1.
Constraints
- 1 <= arr.length <= 1000
- -1000 <= arr[i] <= 1000
Approaches
- Sort and measure runs — time O(n log n), space O(n)
Follow-up
If the answer is false, how few elements would you have to delete to make every count unique? And which values have a count that no other value shares?
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