二分查找的递归写法

package 蓝桥杯1;

public class ERFGDG {
	//int mid;
	public static void main(String[] args) {
		int ar[]= {1,5,6,8,10,22,33,66,89,90};
		System.out.print(a(ar,0,0,ar.length-1));
		
	}
static int a(int arr[],int key,int start,int end) {
	int mid;
	if(start>end) return -1;
	 
	else {  mid=(start+end)>>>1;
	if(key>arr[mid]) 
		return a(arr,key,mid+1,end);
	else if(key==arr[mid])
		return mid;
	else if(key<arr[mid]) 
		return a(arr,key,start,mid-1);}
	return -1;
	
}
}
改
package 蓝桥杯1;

public class ERFGDG {
	//int mid;
	public static void main(String[] args) {
		int ar[]= {1,5,6,8,10,22,33,66,89,90};
		System.out.print(a(ar,8,0,ar.length-1));
		
	}
static int a(int arr[],int key,int start,int end) {
	
	if(start>end) return -1;
	 
	 int mid=(start+end)>>>1;
	if(key>arr[mid]) 
		return a(arr,key,mid+1,end);
	else if(key==arr[mid])
		return mid;
	else  
		return a(arr,key,start,mid-1);

	
}
}

这样，就考虑了所以情况，不用在最后写return -1
mid可定义在成员变量中，因为每次都是先计算值给他，再判断