public static int sockMerchant(int n, List<Integer> ar) {
    Map<Integer, Integer> sockMap = new HashMap<>();
    
    //Perform counting socks
    for(int sock : ar) {
        int frequency = sockMap.getOrDefault(sock, 0);
        sockMap.put(sock, frequency + 1);
    }
    
    int pairs = 0;
    for(int frequency : sockMap.values()) {
        if(frequency >= 2) pairs += frequency/2;
    }
    
    return pairs;
}