二分法查找


二分法查找的前提数组是有序的


 1 package test;
 2 
 3 public class BinarySearch {
 4     public static void main(String[] args) {
 5         int[] arr = new int[] { 12, 23, 34, 45, 56, 67, 77, 89, 90 };
 6         int key = 89;
 7         int target = search(arr, key);
 8         if (target == -1) {
 9             System.out.println("数组中没有此数");
10         } else {
11             System.out.println(key + "在数组arr第" + target + "位");
12         }
13 
14     }
15 
16     public static int search(int[] arr, int key) {
17         int minIndex = 0;
18         int maxIndex = arr.length - 1;
19         int middleIndex = (minIndex + maxIndex) / 2;
20         while (minIndex <= maxIndex) {
21             if (key < arr[middleIndex]) {
22                 maxIndex = middleIndex - 1;
23             } else if (key > arr[middleIndex]) {
24                 minIndex = middleIndex + 1;
25             } else {
26                 return middleIndex;
27             }
28         }
29         return -1;
30     }
31 }