如何修复代码，使其可以使用 for-loop 运行 5 次？

Question

我试图用五个不同的数字运行 5 次（随机，参见 int x），它运行 1 次没有任何问题。 我尝试添加一个 for 循环（带有 // 的行），结果变得一团糟。 我能做些什么来修复它？

示例结果：--> 我能做些什么来修复它？

My code will print the following:
          Trial       Number of Elements      Search Key    ....
            1                65536               123 (random) ....
- - - - - - - - - - - - - - - - - - - - - - --  - -- - - - - - - - - 
I want to become the following: 
  Trial       Number of Elements      Search Key
    1                65536               123 (random)
    2                65536               1234 (random)
    3                65536               1123 (random)
    4                65536               11234 (random)
    5                65536               15234 (random)

Answer 1

您需要处理 result = -1 时的情况（当数组中不存在值时）

所以当 result = -1 你试图访问 arr[result - 1] 即 arr[-2]，这显然是一个无效的索引

import java.util.Random;

class BinarySearch {
    private int compareCount;


    int binarySearch(int arr[], int l, int r, int x) { 
       
        if (r >= l) { 
            int mid = l + (r - l) / 2; 
              
            compareCount++;
            if (arr[mid] == x) 
                return mid; 
    
            compareCount++;
            if (arr[mid] > x) 
                return binarySearch(arr, l, mid - 1, x); 

            return binarySearch(arr, mid + 1, r, x); 
        }
        return -1; 
    } 

    
    public static void main(String args[]) 
    { 
        

        for (int i = 0; i<5;i++) {
            
            BinarySearch ob = new BinarySearch();     
            int[] arr = new Random().ints(65536, 1, 65536 + 1).sorted().toArray();
            
            int n = arr.length; 

            Random rand = new Random();
            int max_range = 65536;
            
            int x = rand.nextInt(max_range); // generate a random number between 1-65536
            System.out.println(x);

            int result = ob.binarySearch(arr, 0, n - 1, x);
            
            String isFound = "N";
            if (result != -1)
                isFound = "Y";
            

            int N = 65536; 
            int expect = (int)(Math.log(N) / Math.log(2)) + 1; 
            
              
          if(result != -1){
                int right_index = 0;
                if(result+1 == max_range) {
                    right_index = arr[result];
                }
                else {
                    right_index = arr[result + 1];
                }

                int left_index = 0;
                if(result == 0) {
                    left_index = arr[0];
                }
                else {
                    left_index = arr[result + 1];
                }

                System.out.println
                ("   Trial    "  +   "   Number of Elements   " +  "   Search Key   " + "   Left Index  " + "   Right Index  " + "    Found/Not Found   " + " Expected Comparision  " + "   Acutal Comparsion   "   + "\n" 
                +"     " + (i + 1) + "              "  +  arr.length +  "              " + x  +   "         " + left_index + "      " + right_index +  "              " + isFound  + "            " + expect + "                   "+  ob.compareCount);
            }
            else {
                System.out.println
                ("   Trial    "  +   "   Number of Elements   " +  "   Search Key   " + "   Left Index  " + "   Right Index  " + "    Found/Not Found   " + " Expected Comparision  " + "   Acutal Comparsion   "   + "\n" 
                +"     "+(i+ 1)+"              "  +  arr.length +  "              " + x  +   "         " + "NOT FOUND" + "      " + "NOT FOUND" +  "              " + isFound  + "            " + expect + "                   "+  ob.compareCount);
            }
            
     }
        
    }
} 

Answer 2

由于您的 BinarySearch object 包含“compareCount”，我认为您将 for 循环添加到了最后一行...每次运行都可能创建一个新的 BinarySearch() 来重置 compareCount。

所以向上移动循环。

如果您发现，您的左/右索引也可以产生超出范围的索引

• 第一个元素
• 最后一个元素
• 没有元素

您可以像这样修复日志记录：

• （结果 > 0？arr[result - 1]：“未找到”）
• （结果 < 最大范围？arr[result + 1]：“未找到”）