Java : How to make this hash table function work on a much larger scale

Question

我有以下代码，它将获取 30 个字符串(即数字)，并在使用“%29”计算它们后将它们放入哈希表中

import java.util.Arrays;


public class HashFunction {

    String[] theArray;
    int arraySize;
    int itemsInArray = 0;

    public static void main(String[] args) {

        HashFunction theFunc = new HashFunction(30); // this is where you should be able to control the number of spaces availble in the hash table!!!

        // Simplest Hash Function

        // String[] elementsToAdd = { "1", "5", "17", "21", "26" };

        // theFunc.hashFunction1(elementsToAdd, theFunc.theArray);

        // Mod Hash Function
        // This contains exactly 30 items to show how collisions
        // will work

        String[] elementsToAdd2 = { "100", "510", "170", "214", "268", "398",
                "235", "802", "900", "723", "699", "1", "16", "999", "890",
                "725", "998", "978", "988", "990", "989", "984", "320", "321",
                "400", "415", "450", "50", "660", "624" };

        theFunc.hashFunction2(elementsToAdd2, theFunc.theArray);

        // Locate the value 660 in the Hash Table

        //theFunc.findKey("660");

        theFunc.displayTheStack();

    }

    // Simple Hash Function that puts values in the same
    // index that matches their value

    public void hashFunction1(String[] stringsForArray, String[] theArray) {

        for (int n = 0; n < stringsForArray.length; n++) {

            String newElementVal = stringsForArray[n];

            theArray[Integer.parseInt(newElementVal)] = newElementVal;

        }

    }



    public void hashFunction2(String[] stringsForArray, String[] theArray) {

                        int sumOfCollisions = 0;
                        float averageOfCollisions = 0;
                        int numberOfCollisions = 0;                        

        for (int n = 0; n < stringsForArray.length; n++) {

            String newElementVal = stringsForArray[n];

            // Create an index to store the value in by taking
            // the modulus

            int arrayIndex = Integer.parseInt(newElementVal) % 29;

            System.out.println("Modulus Index= " + arrayIndex + " for value "
                    + newElementVal);

            // Cycle through the array until we find an empty space


            while (theArray[arrayIndex] != "-1") {
                ++arrayIndex;
                                numberOfCollisions++;

                //System.out.println("Collision Try " + arrayIndex + " Instead");
                                //System.out.println("Number of Collisions = " + numberOfCollisions);
                // If we get to the end of the array go back to index 0

                arrayIndex %= arraySize;
            }


                        if (numberOfCollisions > 0)
                        {
                            System.out.println("                       Number of Collisions = " + numberOfCollisions);
                        }                       

            theArray[arrayIndex] = newElementVal;

        }

                        sumOfCollisions += numberOfCollisions;

                        averageOfCollisions = sumOfCollisions / 30;

                        System.out.println("Sum of Collisions = " + sumOfCollisions);

                        System.out.println("Average of Collisions = " + averageOfCollisions);                

    }

    // Returns the value stored in the Hash Table

    public String findKey(String key) {

        // Find the keys original hash key
        int arrayIndexHash = Integer.parseInt(key) % 29;

        while (theArray[arrayIndexHash] != "-1") {

            if (theArray[arrayIndexHash] == key) {

                // Found the key so return it
                System.out.println(key + " was found in index "
                        + arrayIndexHash);

                return theArray[arrayIndexHash];

            }

            // Look in the next index

            ++arrayIndexHash;

            // If we get to the end of the array go back to index 0

            arrayIndexHash %= arraySize;

        }

        // Couldn't locate the key

        return null;

    }

    HashFunction(int size) {

        arraySize = size;

        theArray = new String[size];

        Arrays.fill(theArray, "-1");

    }

    public void displayTheStack() {

        int increment = 0;

        for (int m = 0; m < 3; m++) {

            increment += 10;

            for (int n = 0; n < 71; n++)
                System.out.print("-");

            System.out.println();

            for (int n = increment - 10; n < increment; n++) {

                System.out.format("| %3s " + " ", n);

            }

            System.out.println("|");

            for (int n = 0; n < 71; n++)
                System.out.print("-");

            System.out.println();

            for (int n = increment - 10; n < increment; n++) {

                if (theArray[n].equals("-1"))
                    System.out.print("|      ");

                else
                    System.out
                            .print(String.format("| %3s " + " ", theArray[n]));

            }

            System.out.println("|");

            for (int n = 0; n < 71; n++)
                System.out.print("-");

            System.out.println();

        }

    }

}

为方便起见，以下是输出:

    run:
Modulus Index= 13 for value 100
Modulus Index= 17 for value 510
Modulus Index= 25 for value 170
Modulus Index= 11 for value 214
Modulus Index= 7 for value 268
Modulus Index= 21 for value 398
Modulus Index= 3 for value 235
Modulus Index= 19 for value 802
Modulus Index= 1 for value 900
Modulus Index= 27 for value 723
Modulus Index= 3 for value 699
                       Number of Collisions = 1
Modulus Index= 1 for value 1
                       Number of Collisions = 2
Modulus Index= 16 for value 16
                       Number of Collisions = 2
Modulus Index= 13 for value 999
                       Number of Collisions = 3
Modulus Index= 20 for value 890
                       Number of Collisions = 3
Modulus Index= 0 for value 725
                       Number of Collisions = 3
Modulus Index= 12 for value 998
                       Number of Collisions = 3
Modulus Index= 21 for value 978
                       Number of Collisions = 4
Modulus Index= 2 for value 988
                       Number of Collisions = 7
Modulus Index= 4 for value 990
                       Number of Collisions = 9
Modulus Index= 3 for value 989
                       Number of Collisions = 14
Modulus Index= 27 for value 984
                       Number of Collisions = 15
Modulus Index= 1 for value 320
                       Number of Collisions = 23
Modulus Index= 2 for value 321
                       Number of Collisions = 31
Modulus Index= 23 for value 400
                       Number of Collisions = 31
Modulus Index= 9 for value 415
                       Number of Collisions = 37
Modulus Index= 15 for value 450
                       Number of Collisions = 40
Modulus Index= 21 for value 50
                       Number of Collisions = 43
Modulus Index= 22 for value 660
                       Number of Collisions = 47
Modulus Index= 15 for value 624
                       Number of Collisions = 61
Sum of Collisions = 61
Average of Collisions = 2.0
-----------------------------------------------------------------------
|   0  |   1  |   2  |   3  |   4  |   5  |   6  |   7  |   8  |   9  |
-----------------------------------------------------------------------
| 725  | 900  |   1  | 235  | 699  | 988  | 990  | 268  | 989  | 320  |
-----------------------------------------------------------------------
-----------------------------------------------------------------------
|  10  |  11  |  12  |  13  |  14  |  15  |  16  |  17  |  18  |  19  |
-----------------------------------------------------------------------
| 321  | 214  | 998  | 100  | 999  | 415  |  16  | 510  | 450  | 802  |
-----------------------------------------------------------------------
-----------------------------------------------------------------------
|  20  |  21  |  22  |  23  |  24  |  25  |  26  |  27  |  28  |  29  |
-----------------------------------------------------------------------
| 890  | 398  | 978  | 400  |  50  | 170  | 660  | 723  | 984  | 624  |
-----------------------------------------------------------------------
BUILD SUCCESSFUL (total time: 0 seconds)

正如您所看到的，我对其进行了设置，以便它告诉我构建此特定哈希表时发生的平均冲突数。它们有 30 个数字和 30 个空格。我尝试将可用空间量的参数从 30 更改为 60，但这并没有改变任何内容，我想知道如何解决此问题。

这对我来说很重要，因为我想让这段代码更上一层楼。我想尝试这个程序来处理更大的数字集，也许是一千个或更多，但我不想只手动输入一千个以上的字符串数字。我该如何编写一个循环来为我做这件事？例如，如果我在其参数中输入 1000，它将生成将使用的一千个字符串表示法数字(如代码中所示)。

我还想这样做，以便我可以在单个程序执行中运行多个这些字符串数字。例如，哈希表可以容纳 1000 个数字，因此它将用 1 个数字运行程序，然后是 2,3，等等...直到它一直运行到 1000。每次执行此操作时，我希望它输出该特定运行中发生的平均碰撞次数。只有 1 个数字不会发生碰撞，随着数字数量的增加，最终会发生碰撞。

通过这样做，我可以制作一个图表，显示碰撞量如何随着数量与可用点的比率变化而变化。例如，x 轴是平均碰撞次数，y 轴是输入的数字数量与总可用空间的比率(意味着其值范围为 0 到 1.00)

提前感谢所有花时间教我的人。我真的很感激。

Answer 1

要让程序为您随机生成数字，您应该创建一个方法，该方法采用整数参数，循环遍历该大小的数组并插入随机数。

int size_of_hash = Integer.parseInt( args[1] );

上面的代码将从命令行获取一个参数，并使用它来创建一个变量来确定哈希表有多大。您可以使用此变量来创建哈希函数，并且可以使用它来创建数组

你可以调用一个方法

public int[] createRandomArray( int size ) {
    Random r = new Random(); //java.util.Random - this class will randomly generate integers for you
     int random_array = //instantiate the array

     for( int i = 0; i <= size; i++ ) {
         //insert logic
      }

      return random_array;
 }

该方法不完整。最好的学习方法就是实践。这里需要注意的重要一点是，这种方法本质上是执行一个简单的重复任务，并让程序为您完成它。 Javadoc 是了解 Java 生态系统内部新资源的绝佳资源。只需谷歌搜索“javadoc random”，就会出现该类。

我建议将 main 方法更改为类的构造函数，并重写 main 方法以调用您可以在程序参数中指定的大量试验。这将帮助您通过运行大量而不是一次的试验来获得更准确的数据。