# Coding Challenge from Leetcode - Unique Number of Occurrences!

Here is the problem and solution to a coding challenge from

Use a hashmap to store the frequency of each character, then use a set to check for duplicates

**Leetcode.com**called**!**__Unique Number of Occurrences__## Problem

*Given an array of integers arr, return true if the number of occurrences of each value in the array is unique or false otherwise.*## Solution Summary

### Intuition / tip

Use a hashmap to store the frequency of each character, then use a set to check for duplicates

### Steps

- Create a map to hold frequencies
- Loop the input array - for each item either add it to the map with a value of 1, or increment the value if already in the map
- Create a set to use to check for duplicates
- Loop the values in the frequency map
- For each item check if already in the duplicates set, if so, return false (the number of occurrences IS NOT unique). If not, add the item to the duplicate set.
- Return true at the end the function (the number of occurrences IS unique if we get here)

### Time complexity

O(n) where ’n’ is the number of characters of the input array

### Space complexity

O(n) where ’n’ is the number of characters of the input array

Let me know if you have any questions or see ways I could have optimized!

Here is a video of me working through the problem: