int sockMerchant(int n, vector<int> ar) {
    unordered_map<int, int> frequencyMap;
    
    int nPairs = 0;
    
    for(int i = 0; i < ar.size(); ++i){
        frequencyMap[ar[i]] += 1;
        if(frequencyMap[ar[i]] % 2 == 0){
            nPairs +=1;
        }
    }
    
    return nPairs;
}