Challenge: First Non-Repeating Integer in an Array

Problem Statement

In this problem, you have to implement the int findFirstUnique(int[] arr) function that will look for a first unique integer which appears only once in the whole array. You must use hashing to implement this function in the most optimized way possible.

Note: We consider zero to be an integer for the premise of this challenge.

Function Prototype

int findFirstUnique(int[] arr)

Output

The first unique element in the array.

Sample Input

arr = {9, 2, 3, 2, 6, 6}

Sample Output

9