同事写的二分归并排序

package Sort;

/**

* 二分归并排序，平均划分数组，递归划分，合并

*

* @author lucky-django

*

*/

public class MergeSort {

/**

* 合并操作

*/

public void merge(int[] array, int startIndex, int midIndex, int endIndex) {

int x = midIndex - startIndex;// 前一个数组的最大index

int y = endIndex - midIndex - 1;// 后一个数组的最大index

int[] firstArray = new int[midIndex - startIndex + 1];

int[] secondArray = new int[endIndex - midIndex];

// 将原数组复制到两个子数组中

for (int i = 0; i <= x; i++) {

firstArray[i] = array[i + startIndex];

}

for (int i = 0; i <= y; i++) {

secondArray[i] = array[i + midIndex + 1];

}

int i = 0, j = 0, k = startIndex;

while (i <= x && j <= y) {

if (firstArray[i] <= secondArray[j]) {

array[k] = firstArray[i];

i++;

} else {

array[k] = secondArray[j];

j++;

}

k++;

}

if (i > x) {

for (; j <= y; j++) {

array[k] = secondArray[j];

k++;

}

} else {

for (; i <= x; i++) {

array[k] = firstArray[i];

k++;

}

}

}

/**

* 划分+合并

*/

public void mergeSort(int[] array, int startIndex, int endIndex) {

if (startIndex >= endIndex) {

return;

}

int mid = (startIndex + endIndex) / 2;

mergeSort(array, startIndex, mid);

mergeSort(array, mid + 1, endIndex);

merge(array, startIndex, mid, endIndex);

}

public static void main(String[] args) {

int[] array = new int[] { 8, 2, 4, 6 };

MergeSort sort = new MergeSort();

sort.mergeSort(array, 0, 3);

for (int i = 0; i < array.length; i++) {

System.out.println(array[i]);

}

}

}