Java排序算法之归并排序简单实现

package sorting;
/**
 * 归并排序
 * 平均O(nlogn),最好O(nlogn),最坏O(nlogn);空间复杂度O(n);稳定;较复杂
 * @author zeng
 *
 */
public class MergeSort {
	public static void merge(int[] a, int start, int mid,
	      int end) {
		int[] tmp = new int[a.length];
		System.out.println("merge " + start + "~" + end);
		int i = start, j = mid + 1, k = start;
		while (i != mid + 1 && j != end + 1) {
			if (a[i] < a[j])
			        tmp[k++] = a[i++]; else
			        tmp[k++] = a[j++];
		}
		while (i != mid + 1)
		      tmp[k++] = a[i++];
		while (j != end + 1)
		      tmp[k++] = a[j++];
		for (i = start; i <= end; i++)
		      a[i] = tmp[i];
		for (int p : a)
		      System.out.print(p + " ");
		System.out.println();
	}
	static void mergeSort(int[] a, int start, int end) {
		if (start < end) {
			int mid = (start + end) / 2;
			mergeSort(a, start, mid);
			// 左边有序
			mergeSort(a, mid + 1, end);
			// 右边有序
			merge(a, start, mid, end);
		}
	}
	public static void main(String[] args) {
		int[] b = { 49, 38, 65, 97, 76, 13, 27, 50 };
		mergeSort(b, 0, b.length - 1);
	}
}