二分法查找

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1. /// <summary> 
2.         /// 二分查找算法 
3.         /// </summary> 
4.         /// <param name="arr">要查找的数组</param> 
5.         /// <param name="sel">要查找的值</param> 
6.         /// <returns></returns> 
7.         protected string GetValue(string[] arr, string sel) 
8.         { 
9.             int langth = arr.Length;//数组的长度 
10.             int min = 0;//要查找的数组的下限 
11.             int max = langth - 1;//要查找的数组的上限 
12.             int index = (max - min) / 2 + min;//要查找的索引 
13.             string returnValue = "";//最后要返回的值 
14.             int flag = 0;//比较的时候，之前的那个index 
15.             if (int.Parse(sel) == int.Parse(arr[min].ToString())) 
16.             { 
17.                 returnValue = "最小值和要查的值一样，是：" + min.ToString(); 
18.             } 
19.             else if (int.Parse(sel) == int.Parse(arr[max].ToString())) 
20.             { 
21.                 returnValue = "最大值和要查的值一样，是：" + max.ToString(); 
22.             } 
23.             else if (int.Parse(sel) > int.Parse(arr[langth - 1].ToString()))
24.             { 
25.                 returnValue = "大于最大值了"; 
26.             } 
27.             else if (int.Parse(sel) < int.Parse(arr[0].ToString())) 
28.             { 
29.                 returnValue = "小于最小值了"; 
30.             } 
31.             else 
32.             { 
33.                 do 
34.                 { 
35.                     if (int.Parse(arr[index].ToString()) == int.Parse(sel)) 
36.                     { 
37.                         returnValue += "找到了：" + arr[index].ToString() + " 
38. "; 
39.   
40.                     } 
41.                     else if (int.Parse(arr[index].ToString()) > int.Parse(sel)) 
42.                     { 
43.                         max = index; 
44.                         flag = index; 
45.                         index = (max - min) / 2 + min; 
46.                         returnValue += "是数组中的" + arr[flag].ToString() + "和" + sel + "比较，数组的比较值大了，找前面一个表：" + arr[min].ToString() + "到" + arr[max].ToString() + " 
47. "; 
48.                     } 
49.                     else if (int.Parse(arr[index].ToString()) < int.Parse(sel)) 
50.                     { 
51.                         min = index; 
52.                         flag = index; 
53.                         index = (max - min) / 2 + min; 
54.                         returnValue += "是数组中的" + arr[flag].ToString() + "和" + sel + "比较，数组的比较值小了，找后面一个表：" + arr[min].ToString() + "到" + arr[max].ToString() + " 
55. "; 
56.                     } 
57.                     if (max - min <= 1) 
58.                     { 
59.                         returnValue += "找不到"; 
60.                         break; 
61.                     } 
62.                 } while (int.Parse(arr[index].ToString()) != int.Parse(sel)); 
63.             } 
64.   
65.             //防止那种，在更改过索引值之后，正好索引的值和要查找的值相等的情况 
66.             if (int.Parse(arr[index].ToString()) == int.Parse(sel)) 
67.             { 
68.                 returnValue += "找到了：" + index.ToString() + " 
69. "; 
70.             } 
71.   
72.             return returnValue; 
73.         }