归并排序 java_分治算法——归并排序的java实现

/**

* 归并操作的实现类

*/

public class MergerSorter {

private static final int[] ARRAY = {2, 5, 10, 30, 60, 40, 5, 6, 66};

public int[] sort(int[] array) {

if (array.length == 1)

return array;

final int dividePos = array.length / 2;

int[] array1 = new int[dividePos];

System.arraycopy(array, 0, array1, 0, array1.length);

int[] array2 = new int[array.length - dividePos];

System.arraycopy(array, dividePos, array2, 0, array2.length);

return merge(sort(array1), sort(array2));

}

public int[] merge(int[] a1, int[] a2) {

int[] result = new int[a1.length + a2.length];

int cursor = 0;

int cursor1 = 0;

int cursor2 = 0;

while (cursor1 < a1.length && cursor2 < a2.length) {

if (a1[cursor1] > a2[cursor2]) {

result[cursor++] = a2[cursor2++];

} else {

result[cursor++] = a1[cursor1++];

}

}

while (cursor1 < a1.length) {

result[cursor++] = a1[cursor1++];

}

while (cursor2 < a2.length) {

result[cursor++] = a2[cursor2++];

}

return result;

}

public static void main(String args[]) {

int[] r = new MergerSorter().sort(ARRAY);

for (int t : r) {

System.out.print(t + ",");

}

}

}

MergerSorterTest.java

import static org.junit.Assert.assertArrayEquals;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

/**

* TestCase of MergerSorter

*/

public class MergerSorterTest {

private MergerSorter mergerSorter = null;

@Before

public void setUp() throws Exception {

mergerSorter = new MergerSorter();

}

@After

public void tearDown() throws Exception {

mergerSorter = null;

}

@Test

public void merge() {

int[] a1 = {2, 6, 8, 9};

int[] a2 = {5, 8, 10, 12};

int[] expected = {2, 5, 6, 8, 8, 9, 10, 12};

assertArrayEquals(expected, mergerSorter.merge(a1, a2));

}

@Test

public void sort() {

int[] srcArray = {9, 12, 6, 10, 8, 2, 8, 5};

int[] expected = {2, 5, 6, 8, 8, 9, 10, 12};

assertArrayEquals(expected, mergerSorter.sort(srcArray));

}

}

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2009-08-05 09:08

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评论

2 楼

luckaway

2009-10-11

ivyloo 写道

分治并没要求小的部分和原问题性质相同，你把分治思想和递归搞混了！

呵呵，这倒没仔细考虑，这里的重点是归并排序的实现。

1 楼

ivyloo

2009-10-10

分治并没要求小的部分和原问题性质相同，你把分治思想和递归搞混了！