Question

我正在编写带有最差运行时间O（n ^ 2）和最佳情况O（n）的冒泡排序算法，以使其具有自适应性。我的想法是添加某种布尔标志变量来控制while循环，以便如果算法过早排序，算法将尽早停止。但是，它一直使我的JUnit测试失败。我认为这是我实现布尔变量的方式，但是我不确定将其放在哪里。任何贡献将不胜感激。

    public static<T> void bubbleSort(T[] arr, Comparator<T> comparator) {
        if (arr == null || comparator == null) {
            throw new IllegalArgumentException("Comparator nor array can be null.");
        }
        boolean swapped = true;

        while (swapped) {
            swapped = false;
            for (int i = 0; i < arr.length - 1; i++) {
                for (int j = 0; j < arr.length - i - 1, j++) {
                    if (comparator.compare(arr[j], arr[j + 1]) > 0) {
                        T obj = arr[j];
                        arr[j] = arr[j + 1]
                        arr[j + 1] = obj;
                        swapped = true;
                    }
                }
           }
       }
  }

编辑：这是我正在使用的JUNITS。

public class SortingTests {
    private TeachingAssistant[] tas;
    private TeachingAssistant[] tasByName;
    private ComparatorPlus<TeachingAssistant> comp;
    private static final int TIMEOUT = 200;

@Before
public void setUp() {
        tas = new TeachingAssistant[10];
        tas[0] = new TeachingAssistant("Adrianna");
        tas[1] = new TeachingAssistant("Chad");
        tas[2] = new TeachingAssistant("Jackie");
        tas[3] = new TeachingAssistant("Miguel");
        tas[4] = new TeachingAssistant("Ashley");
        tas[5] = new TeachingAssistant("Scott");
        tas[6] = new TeachingAssistant("Tim");
        tas[7] = new TeachingAssistant("Joey");
        tas[8] = new TeachingAssistant("Raymond");
        tas[9] = new TeachingAssistant("Bartosz");
        tasByName = new TeachingAssistant[10];
        tasByName[0] = tas[0];
        tasByName[1] = tas[4];
        tasByName[2] = tas[9];
        tasByName[3] = tas[1];
        tasByName[4] = tas[2];
        tasByName[5] = tas[7];
        tasByName[6] = tas[3];
        tasByName[7] = tas[8];
        tasByName[8] = tas[5];
        tasByName[9] = tas[6];

        comp = TeachingAssistant.getNameComparator();
    }

    @Test(timeout = TIMEOUT)
    public void testBubbleSort() {
        Sorting.bubbleSort(tas, comp);
        assertArrayEquals(tasByName, tas);
        assertTrue("Number of comparisons: " + comp.getCount(),
                comp.getCount() <= 44 && comp.getCount() != 0);
}

Answer 1

如果我对您的理解正确，那么在数组已经排序（或一半排序）的情况下，您希望达到O（n）。如果要提高时间复杂度，则需要执行以下操作：

for (int i = 0; i < arr.length - 1; i++) {
     boolean swapped = false;
     for (int j = 0; j < arr.length - i - 1, j++) {
          if (comparator.compare(arr[j], arr[j + 1]) > 0) {
              T obj = arr[i];
              arr[i] = arr[i + 1]
              arr[i + 1] = obj;
              swapped = True;
          }
     }
     if (swapped == false)
         break; // no inner swap done so can exit the upper loop
}

Answer 2

怎么样呢？

public static<T> void bubbleSort(T[] arr, Comparator<T> comparator) {

    if (arr == null || comparator == null) {
        throw new IllegalArgumentException("Comparator nor array can be null.");
    boolean swapped = true;

    while (swapped) {
        swapped = false;
        for (int i = 0; i < arr.length - 1; i++) {
            if (comparator.compare(arr[i], arr[i + 1]) > 0) {
                T obj = arr[i];
                arr[i] = arr[i + 1]
                arr[i + 1] = obj;
                swapped = true;
            }
       }
   }


 }

冒泡排序自适应（Java）

2 个答案: