二叉树相关知识总结（二）

二叉树的Java实现

一、分析

一个二叉树节点包含三个部分，分别是，指向左子树的部分，指向右子树的部分，数据部分，如下图所示：

我们是否可以将每个节点都抽象为一个节点对象？

我们下面来尝试下

二、代码实现

package com.example.demo.dataStructure.binaryTree;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class BinaryTree {
    
    List<TreeNode> datas = new ArrayList<TreeNode>();
    
    public static void main(String[] args) {
        BinaryTree tree = new BinaryTree();
        Integer array[] = {1,2,3,4,5,6,7,8,9};
        TreeNode node = tree.createBinaryTree(array);
        System.out.println("先根遍历：");
        tree.preOrderTraversal(node.getRoot());
        System.out.println("中根遍历：");
        tree.inOrderTraversal(node.getRoot());
        System.out.println("后根遍历：");
        tree.postOrderTraversal(node.getRoot());
    }
    
    /**
     * 创建二叉树
     */
    public TreeNode createBinaryTree(Object[] obj) {
        TreeNode root = new TreeNode();
        Arrays.asList(obj).stream().forEach(object -> datas.add(new TreeNode(object)));
        for (int parentIndex = 0; parentIndex < obj.length / 2; parentIndex++) {
            // 左孩子
            datas.get(parentIndex).setLeftChild(datas.get(parentIndex * 2 + 1));
            // 右孩子
            if (parentIndex * 2 + 2 < obj.length) {
                datas.get(parentIndex).setRightChild(datas.get(parentIndex * 2 + 2));
            }    
        }
        root.setRoot(datas.get(0));
        return root;
    }
    
    /**
     * 先根遍历
     */
    public void preOrderTraversal(TreeNode tree) {
        if (null == tree) {
            return;
        }
        System.out.print(tree.getData());
        preOrderTraversal(tree.getLeftChild());
        preOrderTraversal(tree.getRightChild());
    }
    
    /**
     * 中根遍历
     */
    public void inOrderTraversal(TreeNode tree) {
        if (null == tree) {
            return;
        }
        inOrderTraversal(tree.getLeftChild());
        System.out.print(tree.getData());
        inOrderTraversal(tree.getRightChild());
    }
    
    /**
     * 后根遍历
     */
    public void postOrderTraversal(TreeNode tree) {
        if (null == tree) {
            return;
        }
        postOrderTraversal(tree.getLeftChild());
        postOrderTraversal(tree.getRightChild());
        System.out.print(tree.getData());
    }
    
    
    class TreeNode {
        private TreeNode leftChild; // 左孩子
        private TreeNode rightChild; // 右孩子
        private Object data; // 数据部分
        private TreeNode root; // 标明根节点
        
        public TreeNode() {
            super();
        }
        
        // 初始化节点
        public TreeNode(TreeNode leftChild, TreeNode rightChild, Object data) {
            super();
            this.leftChild = leftChild;
            this.rightChild = rightChild;
            this.data = data;
        }
        
        // 初始化数据域
        public TreeNode(Object data) {
            this(null, null, data);
        }

        public TreeNode getLeftChild() {
            return leftChild;
        }

        public void setLeftChild(TreeNode leftChild) {
            this.leftChild = leftChild;
        }

        public TreeNode getRightChild() {
            return rightChild;
        }

        public void setRightChild(TreeNode rightChild) {
            this.rightChild = rightChild;
        }

        public Object getData() {
            return data;
        }

        public void setData(Object data) {
            this.data = data;
        }

        public TreeNode getRoot() {
            return root;
        }

        public void setRoot(TreeNode root) {
            this.root = root;
        }
    }
}

package com.example.demo.dataStructure.binaryTree;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class BinaryTree {
    
    List<TreeNode> datas = new ArrayList<TreeNode>();
    
    public static void main(String[] args) {
        BinaryTree tree = new BinaryTree();
        Integer array[] = {1,2,3,4,5,6,7,8,9};
        TreeNode node = tree.createBinaryTree(array);
        System.out.println("先根遍历：");
        tree.preOrderTraversal(node.getRoot());
        System.out.println("中根遍历：");
        tree.inOrderTraversal(node.getRoot());
        System.out.println("后根遍历：");
        tree.postOrderTraversal(node.getRoot());
    }
    
    /**
     * 创建二叉树
     */
    public TreeNode createBinaryTree(Object[] obj) {
        TreeNode root = new TreeNode();
        Arrays.asList(obj).stream().forEach(object -> datas.add(new TreeNode(object)));
        for (int parentIndex = 0; parentIndex < obj.length / 2; parentIndex++) {
            // 左孩子
            datas.get(parentIndex).setLeftChild(datas.get(parentIndex * 2 + 1));
            // 右孩子
            if (parentIndex * 2 + 2 < obj.length) {
                datas.get(parentIndex).setRightChild(datas.get(parentIndex * 2 + 2));
            }    
        }
        root.setRoot(datas.get(0));
        return root;
    }
    
    /**
     * 先根遍历
     */
    public void preOrderTraversal(TreeNode tree) {
        if (null == tree) {
            return;
        }
        System.out.print(tree.getData());
        preOrderTraversal(tree.getLeftChild());
        preOrderTraversal(tree.getRightChild());
    }
    
    /**
     * 中根遍历
     */
    public void inOrderTraversal(TreeNode tree) {
        if (null == tree) {
            return;
        }
        inOrderTraversal(tree.getLeftChild());
        System.out.print(tree.getData());
        inOrderTraversal(tree.getRightChild());
    }
    
    /**
     * 后根遍历
     */
    public void postOrderTraversal(TreeNode tree) {
        if (null == tree) {
            return;
        }
        postOrderTraversal(tree.getLeftChild());
        postOrderTraversal(tree.getRightChild());
        System.out.print(tree.getData());
    }
    
    
    class TreeNode {
        private TreeNode leftChild; // 左孩子
        private TreeNode rightChild; // 右孩子
        private Object data; // 数据部分
        private TreeNode root; // 标明根节点
        
        public TreeNode() {
            super();
        }
        
        // 初始化节点
        public TreeNode(TreeNode leftChild, TreeNode rightChild, Object data) {
            super();
            this.leftChild = leftChild;
            this.rightChild = rightChild;
            this.data = data;
        }
        
        // 初始化数据域
        public TreeNode(Object data) {
            this(null, null, data);
        }

        public TreeNode getLeftChild() {
            return leftChild;
        }

        public void setLeftChild(TreeNode leftChild) {
            this.leftChild = leftChild;
        }

        public TreeNode getRightChild() {
            return rightChild;
        }

        public void setRightChild(TreeNode rightChild) {
            this.rightChild = rightChild;
        }

        public Object getData() {
            return data;
        }

        public void setData(Object data) {
            this.data = data;
        }

        public TreeNode getRoot() {
            return root;
        }

        public void setRoot(TreeNode root) {
            this.root = root;
        }
    }
}

运行结果如下：

下一篇我们研究下，二叉查找树。