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);

 

 }

 

 

    //算法複雜度極高 遍歷 n/2的數據取查找   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;

 

    }

 

 

}