排序算法之归并排序 java

数据通过链表方式存储实现代码如下：

public static ListNode mergeSortList(ListNode head) {
		if(head==null||head.next==null)
	    return head;
		ListNode mid = getMid(head);
		ListNode right = mergeSortList(mid.next);
		mid.next=null;
		ListNode left = mergeSortList(head);
		return merge(left, right);
	}
	public static ListNode getMid(ListNode head){
		
		ListNode p=head;
		ListNode q = p.next;
		while(q!=null&&q.next!=null){
			p=p.next;
			q=q.next.next;
		}
		return p;
	}
	public static ListNode merge(ListNode left,ListNode right){
		ListNode result;
		if(left==null)
			return right;
		if(right==null)
			return left;
		if(left.val<right.val){
			result=left;
			left=left.next;
		}
		else{
			result=right;
			right=right.next;
		}
		ListNode temp=result;
		while(left!=null&&right!=null){
			if(left.val<right.val){
			temp.next=left;
			left=left.next;
			}
			else{
				temp.next=right;
				right=right.next;
			}
			temp=temp.next;
		}
		if(left!=null)
			temp.next=left;
		if(right!=null)
			temp.next=right;
		return result;
	}