二分搜索（非递归）

public class Main{
    public static int binarySearch(int a[],int x,int n) {
        int left=0;
        int right=n-1;
        while(left<=right) {
            int middle=(left+right)/2;
            if(a[middle]==x) {
                return middle;
            }
            if(a[middle]<x) {
                left=middle+1;
            }
            else {
                right=middle-1;
            }
        }
        return -1;
    }
    public static void main(String args[]) {
        int a[]= {1,3,5,7,9};
        System.out.println(binarySearch(a,7,a.length));
    }
}