二叉树的三叉链表存储及其Java实现

三叉链表存储的思想是让每个节点持有三个引用parent、left、right，分别指向其父节点、左子节点和右子节点。如下图所示：

因此，三叉链表存储的节点大致如：

class Node{
        T data;
        Node parent;
        Node left;
        Node right;
    }

Java实现代码：

package com.liuhao.DataStructures;

import com.liuhao.DataStructures.TwoLinkBinTree.TreeNode;

public class ThreeLinkBinTree<E> {

	public static class TreeNode{
		Object data;
		TreeNode parent;
		TreeNode left;
		TreeNode right;
		
		public TreeNode() {
		}
		
		public TreeNode(Object data) {
			this.data = data;
		}

		public TreeNode(Object data, TreeNode parent, TreeNode left,
				TreeNode right) {
			this.data = data;
			this.parent = parent;
			this.left = left;
			this.right = right;
		}
	}
	
	private TreeNode root;
	
	public ThreeLinkBinTree(){
		this.root = new TreeNode();
	}
	
	//以指定元素创建
	public ThreeLinkBinTree(E data){
		this.root = new TreeNode(data);
	}
	
	/**
	 * 为指定节点添加子节点
	 * @param parent 待添加的节点 
	 * @param data 添加子节点的数据
	 * @param isLeft 是否要添加左子节点
	 * @return 新增的节点
	 */
	public TreeNode addNode(TreeNode parent, E data, boolean isLeft){
		if(parent == null){
			throw new RuntimeException(parent + "节点为空，不能添加子节点！");
		}
		
		if(isLeft && parent.left != null){
			throw new RuntimeException(parent + "节点已有左子节点，不能添加左子节点！");
		}
		
		if(!isLeft && parent.right != null){
			throw new RuntimeException(parent + "节点已有右子节点，不能添加右子节点！");
		}
		
		TreeNode newNode = new TreeNode(data);
		if(isLeft){
			parent.left = newNode;
		}else{
			parent.right = newNode;
		}
		
		//让新节点的parent引用指向parent节点
		newNode.parent = parent;
		return newNode;
	}
	
	//判断二叉树是否为空
	public boolean isEmpty(){
		return root.data == null;
	}
	
	//获取根节点
	public TreeNode getRoot(){
		if(isEmpty()){
			throw new RuntimeException("树为空，无法获取根节点！");
		}
	return root;
	}
	
	//获取指定节点的父节点
	public TreeNode getParent(TreeNode node){
		if(node == null){
			throw new RuntimeException("节点为空，无法获取父节点！");
		}
		
		if(root == node){
			throw new RuntimeException("根节点无法获取父节点！");
		}
		
		return node.parent;
	}
	
	//获取指定节点的左子节点
	public TreeNode getLeft(TreeNode parent){
		if(parent == null){
			throw new RuntimeException(parent + "节点为空，不能获取子节点！");
		}
		
		return parent.left == null ? null : parent.left;
	}
	
	//获取指定节点的右子节点
	public TreeNode getRight(TreeNode parent){
		if(parent == null){
			throw new RuntimeException(parent + "节点为空，不能获取子节点！");
		}
		
		return parent.right == null ? null : parent.right;
	}
	
	//获取指定节点的深度
	private int getDeep(TreeNode node){
		if(node == null){
			return 0;
		}
		
		if(node.left == null && node.right == null){
			return 1;
		}else{
			int leftDeep = getDeep(node.left);
			int rightDeep = getDeep(node.right);
			
			int max = leftDeep > rightDeep ? leftDeep : rightDeep;
			return max + 1;
		}
	}
	
	public int getTreeDeep(){
		return this.getDeep(root);
	}
	
}

从上面的代码可以看出，三叉链表存储只是对而二叉链表的改进，通过增加一个parent的引用，可以让每个节点都能方便地访问其父节点。