折半查找
C#
1 // -------------------------------------------------------------------------------------------------------------------- 2 // <copyright company="Chimomo's Company" file="Program.cs"> 3 // Respect the work. 4 // </copyright> 5 // <summary> 6 // The binary search (not recursive). 7 // [折半查找的前提]： 8 // 1、待查找序列必须采用顺序存储结构。 9 // 2、待查找序列必须是按关键字大小有序排列。 10 // </summary> 11 // -------------------------------------------------------------------------------------------------------------------- 12 13 namespace CSharpLearning 14 { 15 using System; 16 17 /// <summary> 18 /// The program. 19 /// </summary> 20 internal class Program 21 { 22 /// <summary> 23 /// Entry point into console application. 24 /// </summary> 25 public static void Main() 26 { 27 int[] a = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; 28 Console.WriteLine(BinarySearch(a, 6, 9)); 29 } 30 31 /// <summary> 32 /// 在长度为n的有序数组a中查找值为key的元素（非递归查找）。 33 /// </summary> 34 /// <param name="a"> 35 /// 待查找数组。 36 /// </param> 37 /// <param name="key"> 38 /// 目标元素。 39 /// </param> 40 /// <param name="n"> 41 /// 数组长度。 42 /// </param> 43 /// <returns> 44 /// 若查找到目标元素则返回该目标元素在数组中的下标；否则返回-1。 45 /// </returns> 46 private static int BinarySearch(int[] a, int key, int n) 47 { 48 int low = 0; 49 int high = n - 1; 50 while (low <= high) 51 { 52 int mid = (low + high) / 2; 53 if (a[mid] == key) 54 { 55 return mid; 56 } 57 58 if (a[mid] < key) 59 { 60 low = mid + 1; 61 } 62 else 63 { 64 high = mid - 1; 65 } 66 } 67 68 return -1; 69 } 70 } 71 } 72 73 // Output: 74 /* 75 5 76 */
