采用二分法

1.假设有一个数组 { 12, 23, 34, 45, 56, 67, 77, 89, 90 }，现要求采用二分法找出指定的数值并将其在数组的索引返回，如果没有找到则返回 -1。代码如下：

package cn.sunzn.dichotomy;

public class DichotomySearch {

   public static void main(String[] args) {

       int[] arr = new int[] { 12, 23, 34, 45, 56, 67, 77, 89, 90 };

       System.out.println(search(arr, 12));

       System.out.println(search(arr, 45));

       System.out.println(search(arr, 67));

       System.out.println(search(arr, 89));

       System.out.println(search(arr, 99));

   }

   public static int search(int[] arr, int key) {

       int start = 0;

       int end = arr.length - 1;

       while (start <= end) {

           int middle = (start + end) / 2;

           if (key < arr[middle]) {

               end = middle - 1;

           } else if (key > arr[middle]) {

               start = middle + 1;

           } else {

               return middle;

           }

       }

       return -1;

   }

}

 

 

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