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++];
}
}