二分法查找数组中元素

要使用二分法需要注意:  数组中的元素必须已经按升序排列好

二分法主要思想是将一个数组一分为二，每次查询都能将查询范围在上一次的基础上缩小一半。所以效率非常高。

下面是Java代码实现:

 1 public class DichotomySearchDemo
 2 {
 3
 4     public static void main(String[] args)throws Exception
 5     {
 6         int[] array = new int[]{1,3,4,6,7,9,10,10,12,18,21,29};
 7         int head = 0;
 8         int tail = array.length-1;
 9         int mid = (head+tail)/2;
10         int target = 10;
11
12         dichotomySearch(array,head,mid,tail,target);
13     }
14
15     public static void dichotomySearch(int[] array,int head,int mid, int tail,int target)
16     {
17         if(array[head] == target)
18         {
19             System.out.println("目标"+target+"已找到,位置:" + head);
20             return;
21         }else if(array[mid] == target)
22         {
23             System.out.println("目标"+target+"已找到,位置:" + mid);
24             return;
25         }else if(array[tail] == target)
26         {
27             System.out.println("目标"+target+"已找到,位置:" + tail);
28             return;
29         }
30
31         if(head == mid || head == tail || mid == tail)
32         {
33             System.out.println("查找失败");
34             return;
35         }
36
37         if(target > array[mid])
38         {
39             head = mid;
40         }
41         else if(target < array[mid])
42         {
43             tail = mid;
44         }
45         mid = (head + tail ) / 2;
46
47         dichotomySearch(array,head,mid,tail,target);
48     }
49 }

输出结果:

目标10已找到,位置:6