Is First Unique Even Element easy or hard?

First Unique Even Element is considered an easy problem. The main idea is recognizing the frequency counting pattern with a hash map and filtering for even numbers while preserving the array's original order.

First Unique Even Element Python/Java solution

Python implementations typically use a dictionary or collections.Counter to track frequencies, while Java solutions use a HashMap . Both follow the same two-pass strategy: count occurrences first, then scan for the first even number with count equal to one.

How to solve First Unique Even Element in O(n)?

Use a hash map to store how many times each number appears. Perform a first pass through the array to build the frequency map. In a second pass, check each number in order and return the first element that is even and has frequency equal to one.

What is the best approach for First Unique Even Element?

The best approach uses a hash map to count frequencies of all numbers in the array. After building the frequency table in one pass, iterate through the array again and return the first value that is even and has a frequency of one. This method runs in O(n) time with O(n) extra space.

Is First Unique Even Element asked at Google/Amazon/Meta?

Problems based on frequency counting and hash maps are common in interviews at companies like Amazon, Google, and Meta. While the exact title may vary, identifying unique elements or first non-repeating values in an array appears frequently in screening rounds.

What data structure is used in First Unique Even Element?

A hash table (hash map or dictionary) is typically used to store element frequencies. This structure provides average O(1) insertion and lookup, which allows the algorithm to check whether a value is unique while scanning the array.

What is the time complexity of First Unique Even Element?

The optimal solution runs in O(n) time because the array is scanned twice: once to count frequencies and once to locate the first unique even value. Hash map lookups are O(1) on average, keeping the total runtime linear. Space complexity is O(n) for storing counts.

3866. First Unique Even Element - Practice Online

You are given an integer array nums.

Return an integer denoting the first even integer (earliest by array index) that appears exactly once in nums. If no such integer exists, return -1.

An integer x is considered even if it is divisible by 2.

Example 1:

Input: nums = [3,4,2,5,4,6]

Output: 2

Explanation:

Both 2 and 6 are even and they appear exactly once. Since 2 occurs first in the array, the answer is 2.

Example 2:

Input: nums = [4,4]

Output: -1

Explanation:

No even integer appears exactly once, so return -1.

Constraints:

1 <= nums.length <= 100
1 <= nums[i] <= 100