折半查找

public class A{

 

    public static void main(String[] args){

 

        int[] nums={-1,1,3,19,55,66};  //降序  66 55  19  3  1  -1

 

        int num=66;

 

        int index=A.getIndex(nums,num);

 

        System.out.println(index);

 

    }

 

 

    //算法复杂度极高  遍历  n/2的数据取查找   折半查找 log2N

 

    public static int getIndex(int[] arr,int num){

 

        int min=0;

 

        int max=arr.length-1;

 

        while(min <=max){

 

            int mid=(min+max)/2;

 

            if(num == arr[mid]){

 

                return mid;

 

            }else if(num < arr[mid]){

 

                max=mid-1;

 

            }else{

 

                min=mid+1;

 

            }

 

        }

 

        return -1;

 

    }

 

 

}