递归方法（二分法）

public class A {

public static void main(String[] args) {

       int[]array= {1,2,3,4,5};
   int index = search(array,-4,0,array.length-1);
   System.out.println(index);
}
}
//递归版的二分法方法
public static int search(int[]array,int key,int left,int right) {
    if(left>right) {
        return -1;
    }
    int middle = (left+right)/2;
    if(key==array[middle]) {
        return middle;
    }else if(key>array[middle]) {
        //比中间数字大，在右边，左边界变成middle+1,右边界不变
        return search(array,key,middle+1,right);
    }else {
        return search(array,key,left,middle-1);
    }

}
}