Java数组的查找方式及二分查找

1. 数组查找

   public class ArraySearchTest {
       public static void main(String[] args) {
           int[] a = new int[]{1, 5, 6, 7, 10, 3, 9};
           int value = 9;
   
           int result = search(a, 9);
   
           if (result > 0) {
               System.out.println("找到了，索引为" + result);
           } else {
               System.out.println("未找到");
           }
       }
   
       public static int search(int[] array, int value) {
           int index = -1;
           for (int i = 0; i < array.length; i++) {
               if (array[i] == value) {
                   index = i;
                   break;
               }
           }
           return index;
       }
   }

2. 二分查找（Binary Search）：待查找的数组必须有序

   1,2,3,4,5,6,7,8,9

   10

   public static int binarySearch(int[] array, int value) {
           int left = 0;
           int right = array.length - 1;
           int middle;
   
           while (left <= right) {
               middle = (left + right) / 2;
   
               for (int k = 0; k < array.length; k++) {
                   System.out.print(array[k]);
                   if (k == middle) {
                       System.out.print("#");
                   }
                   System.out.print(" ");
               }
   
               System.out.println();
   
               if (array[middle] == value) {
                   return middle;
               }
   
               if (value > array[middle]) {
                   left = middle + 1;
               }
   
               if (value < array[middle]) {
                   right = middle - 1;
               }
           }
   
           return -1;
       }

   效果

   1 2 3 4 5
   1 2 3 4 5 6 7
   1 2 3 4 5 6 7 8
   1 2 3 4 5 6 7 8 9# 
   找到了，索引为8

3. 随机生成50个数字（整数），每个数字的范围是[10,50]，统计每个数字出现的次数以及出现次数最多的数字与它的个数 ，最后将每个数字及其出现次数打印出来，如果某个数字出现次数为 0，则不要打印它。打印时按照数字的升序排列。

   import java.util.Random;
   
   /**
    * @name: WorkTest
    * @author: terwer
    * @date: 2022-10-19 00:10
    **/
   public class WorkTest {
       public static void main(String[] args) {
           int[] nums = new int[50];
   
           Random random = new Random();
           for (int i = 0; i < nums.length; i++) {
               nums[i] = 10 + random.nextInt(50 - 10 + 1);
           }
   
   
           for (int j = 10; j <= 50; j++) {
               int count = 0;
               for (int m = 0; m < nums.length; m++) {
                   if (nums[m] == j) {
                       count++;
                   }
               }
   
               if (count > 0) {
                   System.out.println(j + "出现的次数：" + count);
               }
           }
   
   
   //        for (int k = 0; k < nums.length; k++) {
   //            System.out.println(nums[k]);
   //        }
       }
   }

   更好的实现：

   import java.util.Random;
   
   /**
    * @name: WorkTest
    * @author: terwer
    * @date: 2022-10-19 00:10
    **/
   public class WorkTest2 {
       public static void main(String[] args) {
           int[] count = new int[41];
   
           Random random = new Random();
           for (int i = 0; i < 50; i++) {
               int number = 10 + random.nextInt(50 - 10 + 1);
               System.out.println(number);
               count[number - 10]++;
           }
   
   
           for (int j = 0; j < count.length; j++) {
               if (count[j] == 0) {
                   continue;
               }
   
               System.out.println((10 + j) + "出现的次数：" + count[j]);
           }
   
           int max = count[0];
           int maxNum = 10;
           for (int k = 0; k < count.length; k++) {
               if (max < count[k]) {
                   max = count[k];
               }
   
               if (max == count[k]) {
                   maxNum = k + 10;
                   System.out.println(maxNum);
               }
           }
           System.out.println("最大的数字出现的次数：" + max);
       }
   }

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