如何使用数组，函数和二进制搜索来完成我的作业？

Question

所以基本上我想做的是一个程序，询问用户他希望他的数组有多大，以及用户在数组中引入值。然后我希望用户能够引入一个数字，并且程序可以确定该数字在哪个数组中，或者确定它不存在。以下程序当前随机生成数组的值，用户介绍了他想要使用的数组元素。但我不知道如何将其转化为我之前解释的内容。

package laboratorio9;

import java.util.Random;
import java.util.Arrays;

public class ArregloBinario
{
    private int[] datos;
    private static Random generador = new Random();

    public ArregloBinario (int tamanio)
    {
        datos = new int[tamanio];

        for (int i=0; i<tamanio; i++)
            datos[i] = 10 + generador.nextInt(90);

        Arrays.sort(datos);
    }

    public int busquedaBinaria(int elementoBusqueda)
    {
        int inferior = 0;
        int superior = datos.length-1;
        int medio = (inferior + superior + 1 ) / 2;
        int ubicacion = -1;

        // **HOW CAN I CHANGE THE FOLLOWING NTO A RECURSIVE FUNCTION>**
        do 
        {
            System.out.print(elementosRestantes(inferior,superior));

            for (int i = 0; i<medio; i++)
                System.out.print("  ");
            System.out.println(" * ");

            if (elementoBusqueda == datos[medio])
                ubicacion=medio;
            else if (elementoBusqueda<datos[medio])
                superior = medio-1;
            else 
                inferior = medio+1;

            medio = (inferior + superior + 1) / 2;
        } while ((inferior <=superior) && (ubicacion == -1));
        return ubicacion;                
    }

    public String elementosRestantes(int inferior, int superior)
    {
        StringBuilder temporal = new StringBuilder();

        for (int i = 0; i < inferior; i++)
            temporal.append( "  " );

        for (int i = inferior; i <= superior; i++)
            temporal.append( datos[i] + " ");

        temporal.append("\n");
        return temporal.toString();
    }

    public String toString()
    {
        return elementosRestantes(0, datos.length-1);
    }
}

// MAIN CLASS //

package laboratorio9;

import java.util.Scanner;

public class PruebaBusquedaBinaria {
    public static void main(String[] args)
    {
        Scanner entrada = new Scanner(System.in);

        int enteroABuscar;
        int posicion;

        System.out.println("Please write the number of elements in the array.");
        int number = entrada.nextInt();

        ArregloBinario arregloBusqueda = new ArregloBinario(number);
        System.out.println(arregloBusqueda);

        System.out.print("Write a value (-1) to go out: ");
        enteroABuscar = entrada.nextInt();
        System.out.println();

        while (enteroABuscar != -1)
        {
            posicion = arregloBusqueda.busquedaBinaria(enteroABuscar);

            if (posicion==-1)
                System.out.println("The value " + enteroABuscar + " was not found.\n");
            else
                System.out.println("The value " + enteroABuscar +
                        " was found in position " + posicion + ".\n");

            System.out.print(
                    "Write a number (-1 to go out): ");
            enteroABuscar = entrada.nextInt();
            System.out.println();
        }
    }
}

Answer 1

首先，这是原始的ArregloBinario类，其间距已固定：

package laboratorio9;

import java.util.Random;
import java.util.Arrays;

public class ArregloBinario
{
    private int[] datos;
    private static Random generador = new Random();

    public ArregloBinario (int tamanio)
    {
        datos = new int[tamanio];

        for (int i=0; i<tamanio; i++)
            datos[i] = 10 + generador.nextInt(90);

        Arrays.sort(datos);
    }

    public int busquedaBinaria(int elementoBusqueda)
    {
        int inferior = 0;
        int superior = datos.length-1;
        int medio = (inferior + superior + 1 ) / 2;
        int ubicacion = -1;

        // **HOW CAN I CHANGE THE FOLLOWING NTO A RECURSIVE FUNCTION>**
        do 
        {
            System.out.print(elementosRestantes(inferior,superior));

            for (int i = 0; i<medio; i++)
                System.out.print("   ");
            System.out.println(" * ");

            if (elementoBusqueda == datos[medio])
                ubicacion=medio;
            else if (elementoBusqueda<datos[medio])
                superior = medio-1;
            else 
                inferior = medio+1;

            medio = (inferior + superior + 1) / 2;
        } while ((inferior <=superior) && (ubicacion == -1));
        return ubicacion;                
    }

    public String elementosRestantes(int inferior, int superior)
    {
        StringBuilder temporal = new StringBuilder();

        for (int i = 0; i < inferior; i++)
            temporal.append( "   " );

        for (int i = inferior; i <= superior; i++)
            temporal.append( datos[i] + " ");

        temporal.append("\n");
        return temporal.toString();
    }

    public String toString()
    {
        return elementosRestantes(0, datos.length-1);
    }
}

这是一个递归版本：

package laboratorio9;

import java.util.Random;
import java.util.Arrays;

public class ArregloBinario
{
    private int[] datos;
    private static Random generador = new Random();

    public ArregloBinario (int tamanio)
    {
        datos = new int[tamanio];

        for (int i=0; i<tamanio; i++)
            datos[i] = 10 + generador.nextInt(90);

        Arrays.sort(datos);
    }

    private int recursive (int elem, int inf, int sup, int med) {
        System.out.print(elementosRestantes(inf,sup));

        for (int i = 0; i<med; i++)
            System.out.print("   ");
        System.out.println(" * ");

        if (inf > sup)
            return -1;

        if (elem == datos[med])
            return med;

        if (elem<datos[med])
            return recursive (elem,inf,med-1,(inf + med) / 2);

    return recursive (elem,med+1,sup,(med + sup + 2) / 2);
    }

    public int busquedaBinaria(int elementoBusqueda)
    {
        int inf = 0;
        int sup = datos.length-1;
        int med = (inf + sup + 1 ) / 2;
        int ubi = -1;

        return recursive (elementoBusqueda,inf,sup,med);
    }

    public String elementosRestantes(int inferior, int superior)
    {
        StringBuilder temporal = new StringBuilder();

        for (int i = 0; i < inferior; i++)
            temporal.append( "   " );

        for (int i = inferior; i <= superior; i++)
            temporal.append( datos[i] + " ");

        temporal.append("\n");
        return temporal.toString();
    }

    public String toString()
    {
        return elementosRestantes(0, datos.length-1);
    }
}

这是在Eclipse下运行的示例，作为它经历的密集测试： - ）

Please write the number of elements in the array.
20
14 18 19 20 22 31 43 50 55 58 58 59 62 71 72 74 85 92 95 98 

Write a value (-1) to go out: 95
14 18 19 20 22 31 43 50 55 58 58 59 62 71 72 74 85 92 95 98 
                               * 
                                 59 62 71 72 74 85 92 95 98 
                                              * 
                                                85 92 95 98 
                                                       * 
The value 95 was found in position 18.

Write a number (-1 to go out): -1

Answer 2

import java.util.Scanner;
import java.util.Arrays;
public class tester
{
    public static void main(String[] args)
    {
        int randomNums[];
        Scanner myScanner = new Scanner(System.in);
        int len = myScanner.nextInt();

        //create the array with length determined from input
        randomNums = new int[len];

        //populates the array with random numbers
        for(int y=0;y<len;y++)
        {
            randomNums[y] = (int)(Math.random()*50+1);
            System.out.println(randomNums[y]);
        }

        Arrays.sort(randomNums);
        int index=0;
        while(true)
        {
            int searchFor = myScanner.nextInt();
            //input of -1 will end search
            if (searchFor==-1)
                break;
            else
            {
                 index = rBinarySearch(randomNums,0,len,searchFor); 
            }
            if (index==-1)
                System.out.println("not found");
            else
                System.out.println("the element was found at index: " + index);
        }
    }

    public static int rBinarySearch(int[] sorted, int first, int upto, int key) {

        if (first < upto) {
            int mid = first + (upto - first) / 2;  // Compute mid point.
            if (key < sorted[mid]) {
                return rBinarySearch(sorted, first, mid, key);

            } else if (key > sorted[mid]) {
                return rBinarySearch(sorted, mid+1, upto , key);

            } else {
                return mid;   // Found it.
            }
        }
        return -(first + 1);  // Failed to find key
    }
}