二分法查找算法

package SuanFa;

import java.text.SimpleDateFormat;
import java.util.Date;

public class Demo1 {
    public static void main(String []args){

         int []arr={1,3,5,7,9,11,12,13,15,16,18,19,20};
         int a=rank(100,arr);
         System.out.println(a);

         System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(new Date()));
    }

    static int  rank(int key,int []arr){
    int start=0;
    int end=arr.length-1;

    while (start<=end){
        int mid=start+((end-start)/2);
        if(key<arr[mid])end=mid-1;
        else  if(key>arr[mid])start=mid+1;
        else  return  mid;
    }
        return -1;
    }
}