Most Frequent Even Element

Problem Description

Given an integer array nums, return the most frequent even element. If there is a tie, return the smallest one. If there is no such element, return -1.

Key Insights

• The problem requires identifying even numbers from the array and counting their occurrences.
• If multiple even numbers have the same highest frequency, the smallest even number should be returned.
• If no even number exists, the function should return -1.

Space and Time Complexity

Time Complexity: O(n) - where n is the length of the input array, as we traverse the array to count occurrences. Space Complexity: O(k) - where k is the number of unique even numbers encountered, which in the worst case could be n/2.

Solution

To solve this problem, we can use a hash table (or dictionary) to count occurrences of each even number. The algorithm follows these steps:

1. Initialize a hash table to store the frequency of even numbers.
2. Iterate through the array and populate the hash table with counts of even numbers.
3. Track the maximum frequency and the corresponding even number.
4. If multiple even numbers have the same frequency, keep the smallest one.
5. Return the most frequent even number or -1 if no even numbers were found.

Code Solutions