树的孩子兄弟链表实现

树的孩子兄弟链表存储结构，采用两条链分别连接孩子和兄弟结点。其中，child指向该结点的第一个孩子结点，sibling指向该结点的下一个兄弟结点。

public class Tree {
	private TreeNode root;
	
	private class TreeNode{		//树的孩子兄弟链表结点类
		T data;
		TreeNode child,sibling;	//分别指向孩子、兄弟结点
		
		public TreeNode() {
		}
		
		public TreeNode(T data){
			this(data,null,null);
		}
		
		public TreeNode(T data,TreeNode child,TreeNode sibling){
			this.data = data;
			this.child = child;
			this.sibling = sibling;
		}
	}
	
	public Tree() {
	}
	
	public boolean isEmpty(){
		return this.root == null;
	}
	
	//返回p结点最后一个兄弟结点
	public TreeNode getLastSibling(TreeNode p){
		if(p==null || p.sibling==null)
			return null;
		while(p.sibling!=null)
			p = p.sibling;
		return p;
	}
	
	//返回p结点的最后一个孩子
	public TreeNode getLastChild(TreeNode p){
		if(p==null || p.child==null)
			return null;
		p = p.child;
		while(p.sibling!=null)
			p = p.sibling;
		return p;
	}
	
	//插入x作为根结点
	public void insertRoot(T x){
		this.root = new TreeNode(x,this.root,null);
	}
	
	//插入x作为p结点的最后一个兄弟结点
	public TreeNode insertLastSibling(TreeNode p,T x){
		if(p==null)
			return null;
		while(p.sibling!=null)
			p = p.sibling;
		p.sibling = new TreeNode(x);
		return p.sibling;
	}
	
	//插入x作为p结点的最后一个孩子结点
	public TreeNode insertLastChild(TreeNode p,T x){
		if(p==null)
			return null;
		if(p.child==null){
			p.child = new TreeNode(x);
			return p.child;
		}
		else
			return insertLastSibling(p.child,x);
	}
	
	//先根次序遍历树并返回树的横向凹入表示字符串
	public String toString(){
		return toString(root,"");
	}
	//tab表示缩进量
	private String toString(TreeNode p,String tab){
		if(p==null)
			return "";
		return tab+p.data.toString()+"\n"+toString(p.child,tab+"\t")+toString(p.sibling,tab);//递归调用
	}
	
	public Tree make(){
		Tree tree = new Tree();
		tree.root = new TreeNode("中国");
		tree.insertLastChild(tree.root, "北京市");
		tree.insertLastChild(tree.root, "上海市");
		TreeNode js = tree.insertLastChild(tree.root, "江苏省");
		tree.insertLastChild(js, "南京市");
		tree.insertLastChild(js, "苏州市");
		TreeNode korea = tree.insertLastSibling(tree.root, "韩国");
		tree.insertLastChild(korea,"首尔");
		return tree;
	}
	
	public static void main(String[] args) {
		Tree t = new Tree();
		System.out.println(t.make());
	}
}