代码

public class Test {
   public static void main(String[] args)  {
       int [] a = {1,2,3,4,5,6,7,9};
       boolean flag = exists(a,10);
       System.out.println(flag);

   }
   public static boolean exists(int [] arr, int num){
       if(arr==null || arr.length==0)
           return false;
       int L = 0;
       int R = arr.length-1;
       while (L < R){
           int mid = L + ((R-L)>>1);
           if (arr[mid] == num)
               return true;
           else if(arr[mid] > num)
               R = mid -1;
           else
               L = mid +1;
       }
       return arr[L] == num;
   }
}