二分法查找数组元素是否存在

package day01;

public class Suan02DBExist {
    
    public static final int LAST = -1;
    //前提必须保证是有序数组
    public static boolean isExist(int[] arr,int num){
        //定义头
        int head = 0;
        //定义尾部
        int tail = arr.length-1;
        //定义中间
        int mid = 0;
        while(head<=tail){

            //mid = (head+tail)/2;
            //容易溢出，所以最好写成
            mid = head/2+tail/2;
            //或者写成,>>无符号右移一位等同于除以2
            mid = head + ((tail-head)>>1);

            if(arr[mid]==num){
                return true;
            }else if(arr[mid]>num){
                tail = mid-1;
            }else if(arr[mid]