Solution C#:

    public static int sockMerchant(int n, List<int> ar)
            {
                    int pairCount = 0; 
                    var sockDict = new Dictionary<int , int>();
                    foreach(var item in ar){
                            if(sockDict.ContainsKey(item)){
                                    sockDict[item] += 1;
                            }
                            else {
                                    sockDict[item] = 1;
                            }
                    }

                    foreach(var kvp in sockDict){
                            pairCount+= (int)kvp.Value/2;
                    }

                    return pairCount;
            }