3866. First Unique Even Element

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.

class Solution {
public:
    int firstUniqueEven(vector<int>& nums) {
        unordered_map<int,int> freq;
        for(auto& n : nums) freq[n]++;
        for(auto& n : nums) if(freq[n] == 1 and n % 2 == 0) return n;
        return -1;
    }
};