玩数据结构和算法-排序算法的工具类

排序的工具类用于生成随机数组和有序数组，生成的数组用于测试排序算法，比较不同排序算法的性能。

package C02_Sorting_Basic.S06_Insertion_Sort_Advance;

import java.lang.reflect.Method;
import java.lang.Class;
import java.util.Random;

public class SortTestHelper {

    // SortTestHelper不允许产生任何实例
    private SortTestHelper() {
    }

    // 生成有n个元素的随机数组,每个元素的随机范围为[rangeL, rangeR]
    public static Integer[] generateRandomArray(int n, int rangeL, int rangeR) {

        assert rangeL <= rangeR;

        Integer[] arr = new Integer[n];

        for (int i = 0; i < n; i++)
            arr[i] = new Integer((int) (Math.random() * (rangeR - rangeL + 1) + rangeL));
        return arr;
    }

    // 生成一个近乎有序的数组
    // 首先生成一个含有[0...n-1]的完全有序数组, 之后随机交换swapTimes对数据
    // swapTimes定义了数组的无序程度:
    // swapTimes == 0 时, 数组完全有序
    // swapTimes 越大, 数组越趋向于无序
    public static Integer[] generateNearlyOrderedArray(int n, int swapTimes) {

        Integer[] arr = new Integer[n];
        for (int i = 0; i < n; i++)
            arr[i] = new Integer(i);

        for (int i = 0; i < swapTimes; i++) {
            int a = (int) (Math.random() * n);
            int b = (int) (Math.random() * n);
            int t = arr[a];
            arr[a] = arr[b];
            arr[b] = t;
        }

        return arr;
    }

    // 打印arr数组的所有内容
    public static void printArray(Object[] arr) {

        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]);
            System.out.print(' ');
        }
        System.out.println();

        return;
    }

    // 判断arr数组是否有序
    public static boolean isSorted(Comparable[] arr) {

        for (int i = 0; i < arr.length - 1; i++)
            if (arr[i].compareTo(arr[i + 1]) > 0)
                return false;
        return true;
    }

    // 测试sortClassName所对应的排序算法排序arr数组所得到结果的正确性和算法运行时间
    public static void testSort(String sortClassName, Comparable[] arr) {

        // 通过Java的反射机制，通过排序的类名，运行排序函数
        try {
            // 通过sortClassName获得排序函数的Class对象
            Class sortClass = Class.forName(sortClassName);
            // 通过排序函数的Class对象获得排序方法
            Method sortMethod = sortClass.getMethod("sort", new Class[]{Comparable[].class});
            // 排序参数只有一个，是可比较数组arr
            Object[] params = new Object[]{arr};

            long startTime = System.currentTimeMillis();
            // 调用排序函数
            sortMethod.invoke(null, params);
            long endTime = System.currentTimeMillis();

            assert isSorted(arr);

            System.out.println(sortClass.getSimpleName() + " : " + (endTime - startTime) + "ms");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

---

package C02_Sorting_Basic.S06_Insertion_Sort_Advance;

import java.util.Arrays;

public class Main {

    // 比较SelectionSort和InsertionSort两种排序算法的性能效率
    // 优化后，插入排序比选择排序性能略好
    // 对于有序性强的数组，插入排序远远优于选择排序
    public static void main(String[] args) {

        int N = 20000;

        // 测试1 一般测试
        System.out.println("Test for random array, size = " + N + " , random range [0, " + N + "]");

        Integer[] arr1 = SortTestHelper.generateRandomArray(N, 0, N);
        Integer[] arr2 = Arrays.copyOf(arr1, arr1.length);

        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.SelectionSort", arr1);
        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.InsertionSort", arr2);

        System.out.println();


        // 测试2 有序性更强的测试
        System.out.println("Test for more ordered random array, size = " + N + " , random range [0,3]");

        arr1 = SortTestHelper.generateRandomArray(N, 0, 3);
        arr2 = Arrays.copyOf(arr1, arr1.length);

        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.SelectionSort", arr1);
        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.InsertionSort", arr2);

        System.out.println();


        // 测试3 测试近乎有序的数组
        int swapTimes = 100;
        System.out.println("Test for nearly ordered array, size = " + N + " , swap time = " + swapTimes);

        arr1 = SortTestHelper.generateNearlyOrderedArray(N, swapTimes);
        arr2 = Arrays.copyOf(arr1, arr1.length);

        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.SelectionSort", arr1);
        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.InsertionSort", arr2);

        return;
    }
}

package C02_Sorting_Basic.S06_Insertion_Sort_Advance;

import java.util.Arrays;

public class Main {

    // 比较SelectionSort和InsertionSort两种排序算法的性能效率
    // 优化后，插入排序比选择排序性能略好
    // 对于有序性强的数组，插入排序远远优于选择排序
    public static void main(String[] args) {

        int N = 20000;

        // 测试1 一般测试
        System.out.println("Test for random array, size = " + N + " , random range [0, " + N + "]");

        Integer[] arr1 = SortTestHelper.generateRandomArray(N, 0, N);
        Integer[] arr2 = Arrays.copyOf(arr1, arr1.length);

        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.SelectionSort", arr1);
        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.InsertionSort", arr2);

        System.out.println();


        // 测试2 有序性更强的测试
        System.out.println("Test for more ordered random array, size = " + N + " , random range [0,3]");

        arr1 = SortTestHelper.generateRandomArray(N, 0, 3);
        arr2 = Arrays.copyOf(arr1, arr1.length);

        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.SelectionSort", arr1);
        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.InsertionSort", arr2);

        System.out.println();


        // 测试3 测试近乎有序的数组
        int swapTimes = 100;
        System.out.println("Test for nearly ordered array, size = " + N + " , swap time = " + swapTimes);

        arr1 = SortTestHelper.generateNearlyOrderedArray(N, swapTimes);
        arr2 = Arrays.copyOf(arr1, arr1.length);

        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.SelectionSort", arr1);
        SortTestHelper.testSort("C02_Sorting_Basic.S06_Insertion_Sort_Advance.InsertionSort", arr2);

        return;
    }
}