求集合的交集

给定两个数组，求两个数组的交集。

 1             string[] a = new string[] { "khlin", "hzluo", "jjguo", "hhchen", "jxhan", "lxiao", "jsxiao", "wwang", "lsxie", "lwang" };
 2             string[] b = new string[] { "hzluo", "wcxu", "khlin", "shchen", "wzhang", "jxhan", "lxiao", "lwang" };
 3 
 4             
 5             foreach (string stra in a)
 6                 Console.Write("{0} ", stra);
 7             Console.WriteLine();
 8             foreach (string strb in b)
 9                 Console.Write("{0} ", strb);
10             Console.WriteLine();
11             IList<string> list = new List<string>();
12 
13             //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)
14             foreach (string stra in a)
15             {
16                 foreach (string strb in b)
17                 {
18                     if (stra == strb)
19                     {
20                         list.Add(stra);
21                         break;
22                     }
23                 }
24             }
25             Console.WriteLine("方法一:");
26             foreach (string str in list)
27             {
28                 Console.Write("{0} ", str);
29             }
30             Console.WriteLine();
31 
32             //方法二：利用Hashset
33             list.Clear();
34             HashSet<string> hashset = new HashSet<string>();
35             foreach (string stra in a)
36                 hashset.Add(stra);
37             foreach (string strb in b)
38             {
39                 if (!hashset.Add(strb))//无法加入，说明a也存在，加入交集的集合
40                     list.Add(strb);
41             }
42             Console.WriteLine("方法二:");
43             foreach (string str in list)
44             {
45                 Console.Write("{0} ", str);
46             }
47             Console.WriteLine();
48 
49             //方法三：排序，利用两个游标不断对比，找出相同的元素
50             QuickSort(a, 0, a.Length - 1);
51             QuickSort(b, 0, b.Length - 1);//排序
52             list.Clear();
53             int i, j;
54             i = j = 0;//设置两游标
55             while (i <= a.Length - 1 && j <= b.Length - 1)
56             {
57                 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
58                     j++;
59                 else if (a[i].CompareTo(b[j]) < 0)//同上
60                     i++;
61                 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
62                 {
63                     list.Add(a[i]);
64                     i++;
65                     j++;
66                 }
67             }
68             Console.WriteLine("方法三:");
69             foreach (string str in list)
70             {
71                 Console.Write("{0} ", str);
72             }
73             Console.WriteLine();
74             Console.Read();