Reorder List LeetCode

LeetCode :Reorder List

 public void reorderList(ListNode head) {
	           if(head==null||head.next==null){
	        	    return ;
	           }
	           int len=0;
	           ListNode p=head;
	           ListNode end=head;
	           ListNode q;
	           ListNode next;
	           while(p!=null){
	        	    len++;
	        	    p=p.next;
	           }
	           for(int i=0;i<len>>1;i++){
	        	     end=end.next;
	           }
	           q=end.next;
	           end.next=null;
	           Stack<ListNode> stack = new Stack<ListNode>();
	           while(q!=null){
	        	    stack.push(q);
	        	    q=q.next;
	           }
	           p=head;
	           while(p!=null&&!stack.empty()){
	        	     q=stack.pop();
	        	     next=p.next;
	        	     p.next=q;
	        	     q.next=next;
	        	     p=next;
	           }
	    }