二分搜索（非递归）

 1 public class Main{
 2     public static int binarySearch(int a[],int x,int n) {
 3         int left=0;
 4         int right=n-1;
 5         while(left<=right) {
 6             int middle=(left+right)/2;
 7             if(a[middle]==x) {
 8                 return middle;
 9             }
10             if(a[middle]<x) {
11                 left=middle+1;
12             }
13             else {
14                 right=middle-1;
15             }
16         }
17         return -1;
18     }
19     public static void main(String args[]) {
20         int a[]= {1,3,5,7,9};
21         System.out.println(binarySearch(a,7,a.length));
22     }
23 }