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.
Example 1:
Input: nums = [0,1,2,2,4,4,1]
Output: 2
Explanation:
The even elements are 0, 2, and 4. Of these, 2 and 4 appear the most.
We return the smallest one, which is 2.
Example 2:
Input: nums = [4,4,4,9,2,4]
Output: 4
Explanation: 4 is the even element appears the most.
Example 3:
Input: nums = [29,47,21,41,13,37,25,7]
Output: -1
Explanation: There is no even element.
Constraints:
1 <= nums.length <= 2000
0 <= nums[i] <= 105
Solutions
Solution 1: Hash Table
We use a hash table $cnt$ to count the occurrence of all even elements, and then find the even element with the highest occurrence and the smallest value.
The time complexity is $O(n)$, and the space complexity is $O(n)$. Here, $n$ is the length of the array.