二分查找(JAVA)

public class binarySearch {
    public static void main(String[] args) {
    
        int arr[]={1,2,3,4,5,6,7,8,9};
        int key=9;
        //int result=binarySearchMethod_noDiGui(arr,key);//非递归实现
        int result=binarySearchMethod_DiGui(arr,0,arr.length-1,key);//递归实现
        System.out.println("结果："+result);
    }
    
   public static int  binarySearchMethod_noDiGui(int arr[],int key){
       
       int left =0;
       int right=arr.length-1;
       int mid=(left+right)>>1;
       
       while(left<=right){
          if(arr[mid]==key){
              return mid;
          }else if(arr[mid]>key){
              right=mid-1;
          }else{
              left=mid+1;
          }
          mid=(left+right)>>1;
       }
        return -1;
    }
   
   public static int binarySearchMethod_DiGui(int arr[],int left,int right,int key){
       
       int mid=(left+right)>>1;
       
       if(left>right){
           return -1;
       }
       
       if(arr[mid]==key){
           return mid;
       }else if(arr[mid]>key){
           right=mid-1;
           return binarySearchMethod_DiGui(arr,left,right,key);
       }else{
           left=mid+1;
           return binarySearchMethod_DiGui(arr,left,right,key);
       }
   }
}

 

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