Java中的随机数据集快速排序

问题描述

以下编写的Quicksort代码使用数组的第一个元素作为数据透视表，然后对数组进行排序。现在我想随机选择枢轴而不是第一个，然后对数组进行排序，我被卡住了请告诉我在下面的代码中可以做出哪些更改以获得完美的结果。

The below written code of the Quicksort uses the first element of the array as the pivot and then sorts the array. Now I want to randomly pick up the pivot instead of first one and then sort the array and I am stuck please tell me what changes I can make in the below code to get the perfect results.

import java.util.*;
import javax.swing.JOptionPane;

public class Quicksort {

public static void main(String[] args) {
    String arraylength = JOptionPane.showInputDialog("Enter the length of the array.");

    int a = Integer.parseInt(arraylength);
    if (a == 0) {
        System.out.println("Null Length");
    } else {
        int[] list = new int[a];


        for (int i = 0; i < a; i++) {
            String input = JOptionPane.showInputDialog("Input the number.");
            int c = Integer.parseInt(input);
            list[i] = c;
        }

        System.out.println("Before");
        for (int i = 0; i < list.length; i++) {
            System.out.print(list[i] + " ");
        }
        partition(list, 0, list.length - 1);


        System.out.println("\nAfter partitionaing");
        for (int i = 0; i < list.length; i++) {
            System.out.print(list[i] + " ");
        }
        quickSort(list, 0, list.length - 1);

        System.out.println("\nAfter Sorting");
        for (int i = 0; i < list.length; i++) {
            System.out.print(list[i] + " ");
        }
    }
}

private static int partition(int[] list, int first, int last) {
    int pivot = list[first];
    int low = first + 1;
    int high = last;

    while (high > low) {

        while (low < high && list[low] < pivot) {
            low++;
        }


        while (low < high && list[high] >= pivot) {
            high--;
        }


        if (high > low) {
            int temp = list[high];
            list[high] = list[low];
            list[low] = temp;
        }
    }
    while (high > first && list[high] >= pivot) {
        high--;
    }

    if (pivot > list[high]) {
        list[first] = list[high];
        list[high] = pivot;
        return high;
    } else {
        return first;
    }

}

private static void quickSort(int[] list, int first, int last) {
    if (last > first) {
        int pivotIndex = partition(list, first, last);
        quickSort(list, first, pivotIndex - 1);
        quickSort(list, pivotIndex + 1, last);
    }
}
}

推荐答案

您可以使用来自java：

You can use the Random class from java:

Random rand = new Random();
int num = begin_sub_array + rand.nextInt(end_sub_array - begin_sub_array);

这将从子数组的开头（begin_sub_array）生成一个值到子数组的结尾（ end_sub_array）。您只需要获取变量 num ，并在快速排序算法中作为透视图传递。

This will generate a value from beginning of the sub array (begin_sub_array) to end of the sub array (end_sub_array). You just have to take the variable num, and pass as the pivot in your quicksort algorithm.

int pivot = list[num];

这篇关于Java中的随机数据集快速排序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！