求集合的交集

给定两个数组，求两个数组的交集。

            string[] a = new string[] { "khlin", "hzluo", "jjguo", "hhchen", "jxhan", "lxiao", "jsxiao", "wwang", "lsxie", "lwang" };
            string[] b = new string[] { "hzluo", "wcxu", "khlin", "shchen", "wzhang", "jxhan", "lxiao", "lwang" };

            
            foreach (string stra in a)
                Console.Write("{0} ", stra);
            Console.WriteLine();
            foreach (string strb in b)
                Console.Write("{0} ", strb);
            Console.WriteLine();
            IList<string> list = new List<string>();

            //方法一：两数组遍历，最简单粗暴的做法，时间复杂度为O(N^2)
            foreach (string stra in a)
            {
                foreach (string strb in b)
                {
                    if (stra == strb)
                    {
                        list.Add(stra);
                        break;
                    }
                }
            }
            Console.WriteLine("方法一:");
            foreach (string str in list)
            {
                Console.Write("{0} ", str);
            }
            Console.WriteLine();

            //方法二：利用Hashset
            list.Clear();
            HashSet<string> hashset = new HashSet<string>();
            foreach (string stra in a)
                hashset.Add(stra);
            foreach (string strb in b)
            {
                if (!hashset.Add(strb))//无法加入，说明a也存在，加入交集的集合
                    list.Add(strb);
            }
            Console.WriteLine("方法二:");
            foreach (string str in list)
            {
                Console.Write("{0} ", str);
            }
            Console.WriteLine();

            //方法三：排序，利用两个游标不断对比，找出相同的元素
            QuickSort(a, 0, a.Length - 1);
            QuickSort(b, 0, b.Length - 1);//排序
            list.Clear();
            int i, j;
            i = j = 0;//设置两游标
            while (i <= a.Length - 1 && j <= b.Length - 1)
            {
                if (a[i].CompareTo(b[j]) > 0)//由于是从小到大排序，当前a游标大于b游标，b游标下移一位
                    j++;
                else if (a[i].CompareTo(b[j]) < 0)//同上
                    i++;
                else//找到相同的，加入交集集合，两游标同时下移一位，继续比较
                {
                    list.Add(a[i]);
                    i++;
                    j++;
                }
            }
            Console.WriteLine("方法三:");
            foreach (string str in list)
            {
                Console.Write("{0} ", str);
            }
            Console.WriteLine();
            Console.Read();