数组0元素后置算法

完整算法实现

/**
 * 将数组中0全部后置 eg: [1,2,0,3] --> [1,2,3,0]
 * 
 * @author kangye
 */
public class MoveZerosInArray {

    /**
     * 冒泡实现 O(N^2)
     */
    public void moveSorting(int[] array) {
        validateArray(array);

        boolean swap = true;
        while (swap) {
            swap = false;
            for (int i = 0; i < array.length - 1; i++) {
                if ((array[i] < array[i + 1] && array[i + 1] > 0)) {
                    swap(array, i, i + 1);
                    swap = true;
                }
            }
        }
    }

    /**
     * 优化， O(N)
     */
    public void moveUsingTwoPointers(int[] array) {
        validateArray(array);

        int left = 0;
        int right = array.length - 1;
        while (left < right) {
            if (array[left] == 0 && array[right] != 0) {
                swap(array, left, right);
            }
            if (array[left] != 0) {
                left++;
            }
            if (array[right] == 0) {
                right--;
            }
        }
    }

    private void validateArray(int[] array) {
        if (array == null) {
            throw new IllegalArgumentException("You can't pass a null array as argument.");
        }
    }

    private void swap(int[] array, int a, int b) {
        int temp = array[a];
        array[a] = array[b];
        array[b] = temp;
    }
}

补充一个单元测试,写法注意：

 1. 至于test目录下, 保持包名相同

 2. 类名和原测试类保持一致，增加Test后缀，方法名增加test

 3. 尽量使用junit原声断言，和异常申明（有时间补充一篇单元测试方法）

/**
 * @author kangye
 */
public class MoveZerosInArrayTest {

    private MoveZerosInArray moveZeros;

    @Before
    public void setUp() {
        moveZeros = new MoveZerosInArray();
    }

    @Test(expected = IllegalArgumentException.class)
    public void shouldNotAcceptNullArraysSorting() {
        moveZeros.moveSorting(null);
    }

    @Test
    public void shouldWorkWithAnEmptyArraySorting() {
        int[] array = new int[0];

        moveZeros.moveSorting(array);

        assertArrayEquals(new int[0], array);
    }

    @Test
    public void shouldOrganizeAnArrayFullOfZerosSorting() {
        int[] array = { 0, 0, 0, 0, 0 };

        moveZeros.moveUsingTwoPointers(array);

        int[] expected = { 0, 0, 0, 0, 0 };
        assertArrayEquals(expected, array);
    }

    @Test
    public void shouldOrganizeAnArrayFullOfNonZerosSorting() {
        int[] array = { 1, 1, 1, 1, 1 };

        moveZeros.moveUsingTwoPointers(array);

        int[] expected = { 1, 1, 1, 1, 1 };
        assertArrayEquals(expected, array);
    }

    @Test
    public void shouldOrganizeAnArrayWithZerosAndNonPositiveIntegersSorting() {
        int[] array = { 1, 0, 2, 3, 0 };

        moveZeros.moveUsingTwoPointers(array);

        assertZerosAtRight(array);
    }

    @Test
    public void shouldOrganizeAnArrayWithZerosPositiveAndNegativeIntegersSorting() {
        int[] array = { 1, 0, 2, -3, 0, 0, 0, 0, -1 };

        moveZeros.moveUsingTwoPointers(array);

        assertZerosAtRight(array);
    }

    @Test(expected = IllegalArgumentException.class)
    public void shouldNotAcceptNullArraysWithTwoPointers() {
        moveZeros.moveUsingTwoPointers(null);
    }

    @Test
    public void shouldWorkWithAnEmptyArrayWithTwoPointers() {
        int[] array = new int[0];

        moveZeros.moveUsingTwoPointers(array);

        assertArrayEquals(new int[0], array);
    }

    @Test
    public void shouldOrganizeAnArrayFullOfZerosWithTwoPointers() {
        int[] array = { 0, 0, 0, 0, 0 };

        moveZeros.moveUsingTwoPointers(array);

        int[] expected = { 0, 0, 0, 0, 0 };
        assertArrayEquals(expected, array);
    }

    @Test
    public void shouldOrganizeAnArrayFullOfNonZerosWithTwoPointers() {
        int[] array = { 1, 1, 1, 1, 1 };

        moveZeros.moveUsingTwoPointers(array);

        int[] expected = { 1, 1, 1, 1, 1 };
        assertArrayEquals(expected, array);
    }

    @Test
    public void shouldOrganizeAnArrayWithZerosAndNonPositiveIntegersWithTwoPointers() {
        int[] array = { 1, 0, 2, 3, 0 };

        moveZeros.moveUsingTwoPointers(array);

        assertZerosAtRight(array);
    }

    @Test
    public void shouldOrganizeAnArrayWithZerosPositiveAndNegativeIntegersWithTwoPointers() {
        int[] array = { 1, 0, 2, -3, 0, 0, 0, 0, -1 };

        moveZeros.moveUsingTwoPointers(array);

        assertZerosAtRight(array);
    }

    private void assertZerosAtRight(int[] array) {
        boolean zeroFounded = false;
        for (int i : array) {
            if (zeroFounded) {
                assertEquals(0, i);
            } else if (i == 0) {
                zeroFounded = true;
            }
        }
    }
}