3712. Sum of Elements With Frequency Divisible by K

You are given an integer array nums and an integer k.

Return an integer denoting the sum of all elements in nums whose frequency is divisible by k, or 0 if there are no such elements.

Note: An element is included in the sum exactly as many times as it appears in the array if its total frequency is divisible by k.

class Solution {
public:
    int sumDivisibleByK(vector<int>& nums, int k) {
        unordered_map<int,int>freq;
        for(auto& n : nums) freq[n]++;
        int res = 0;
        for(auto& [x,v] : freq) if(v % k == 0) res += x * v;
        return res;
    }
};