二分查找

public class  arithmetic {
  public static void main(String[] args) {
	 int [] arr={1,2,5,7,9,13,16};
	 int result = binarySerach(9, arr);
	 System.out.println("结果："+result);
}

  public static  int  binarySerach(int ref,  int [] a){
	int low=0;
	int high=a.length-1;
	int mid=0;
	//low<=high,不加等号就会漏数据
	while(low<=high){
		mid=(low+high)/2;
		if (ref==a[mid]) {
			return mid;  //返回查询结果
		}else if (ref<a[mid]) {//查询左半块数据
			high=mid-1;
		}else{//查询右半块数据
			low=mid+1;
		}
	}
	// 没有查询到，输出-1
	  return -1; 
  }
}