java 归并排序

package algorithm;

public class MergeSort {
	public static void main(String[] args) {
		int a[] =new int []{ 5, 3, 6, 2, 1, 9, 4, 8, 7 }; 
		System.out.println("*************start*************");
		print(a);
		System.out.println("*******************************");
		mergeSort(a,0,a.length-1);
		System.out.println("***********later:**********");
		print(a);
	}

	private static void print(int[] a) {
		// TODO Auto-generated method stub
		for(int i=0;i<a.length;i++)
			System.out.print(a[i]+" ");
		System.out.println("");
	}

	private static void mergeSort(int[] a, int i, int j) {
		// TODO Auto-generated method stub
		//递归结束条件
		if(i>=j)
			return ;
		int middle=(i+j)/2;
		// 对左边数组进行递归
		mergeSort(a, i, middle);
		// 对右边数组进行递归
		mergeSort(a, middle+1, j);
		 // 合并  
		merge(a,i,middle,j);
		print(a);
	}

	private static void merge(int[] a, int i, int m, int j) {
		// TODO Auto-generated method stub
		int[] temp = new int[a.length];//临时数组
		int left = i;//临时数组的索引
		int right = m+1;//右数组第一个元素索引
		int le = i;//左数组第一个元素索引
		while( i <= m && right <= j){
			if(a[i] <= a[right])
				temp[left++]=a[i++];
			else
				temp[left++]=a[right++];
		}
		while(i<=m)
			temp[left++]=a[i++];
		while(right<=j)
			temp[left++]=a[right++];
		while(le <= j)
			a[le] = temp[le++];
	}
}