java之二分查找

Posted 2021-06-04 葱爷们儿技术栈

1 package other;
 2 
 3 public class BinarySearch {
 4     /*
 5      * 循环实现二分查找算法arr 已排好序的数组x 需要查找的数-1 无法查到数据
 6      */
 7     public static int binarySearch(int[] arr, int x) {
 8         int low = 0;   
 9         int high = arr.length-1;   
10         while(low <= high) {   
11             int middle = (low + high)/2;   
12             if(x == arr[middle]) {   
13                 return middle;   
14             }else if(x <arr[middle]) {   
15                 high = middle - 1;   
16             }else {   
17                 low = middle + 1;   
18             }  
19         }  
20         return -1;  
21     }
22     //递归实现二分查找
23     public static int binarySearch(int[] dataset,int data,int beginIndex,int endIndex){    
24            int midIndex = (beginIndex+endIndex)/2;    
25            if(data <dataset[beginIndex]||data>dataset[endIndex]||beginIndex>endIndex){  
26                return -1;    
27            }  
28            if(data <dataset[midIndex]){    
29                return binarySearch(dataset,data,beginIndex,midIndex-1);    
30            }else if(data>dataset[midIndex]){    
31                return binarySearch(dataset,data,midIndex+1,endIndex);    
32            }else {    
33                return midIndex;    
34            }    
35        }   
36 
37     public static void main(String[] args) {
38         int[] arr = { 6, 12, 33, 87, 90, 97, 108, 561 };
39         System.out.println("循环查找：" + (binarySearch(arr, 87) + 1));
40         System.out.println("递归查找"+binarySearch(arr,3,87,arr.length-1));
41     }
42 }