一、名词释义

二叉树的遍历方式，根据遍历根节点的顺序不同，分为三种：前序(先序)遍历(DLR)、中序遍历(LDR)、后序遍历(LRD)。

【D:degree,节点拥有的子树的个数被称为节点的度，比如二叉树中每个有子树的父节点，都是有度的节点。 L:left R:right】

1、前序遍历【根-左-右】

2、中序遍历【左-根-右】

3、后序遍历【左-右-根】

4、镜像反转【将二叉树的每个左右子树互换】

二、执行代码

package com.dylanu.algorithm;

class BinaryTree{
	BinaryTree left;
	BinaryTree right;
	Integer val;
	public BinaryTree(Integer val) {
		super();
		this.val = val;
	}
	public BinaryTree getLeft() {
		return this.left;
	}
	public BinaryTree getRight() {
		return this.right;
	}
	public Integer getVal() {
		return this.val;
	}
}

public class BinaryTreeTest {
	static StringBuilder stringBuilder = new StringBuilder();
	
	/**先序遍历《 根-左-右 》*/
	public static void preOrderTraversal(BinaryTree root) {
		if(null == root) {
			return;
		}
		//根
		stringBuilder.append(root.getVal()).append("#");
		//左
		preOrderTraversal(root.left);
		//右
		preOrderTraversal(root.right);
	}
	
	/**中序遍历《 左-根-右 》*/
	public static void inOrderTraversal(BinaryTree root) {
		if(null == root ) {
			return;
		}
		inOrderTraversal(root.getLeft());	
		stringBuilder.append(root.getVal()).append("#");
		inOrderTraversal(root.getRight());
	}
	
	/**后序遍历《 左-右-根 》*/
	public static void postOrderTraversal(BinaryTree root) {
		if(null == root ) {
			return;
		}
		postOrderTraversal(root.getLeft());	
		postOrderTraversal(root.getRight());
		stringBuilder.append(root.getVal()).append("#");
	}
	
	/**镜像翻转*/
	public static void reversal(BinaryTree root) {
		if(null == root ) {
			return;
		}
		BinaryTree left = root.getLeft(); 
		BinaryTree right = root.getRight(); 
		reversal(left);
		reversal(right);
		root.left = right;
		root.right = left;
	}
	
	public static void main(String[] args) {
		BinaryTree root = new BinaryTree(6);
		
		root.left = new BinaryTree(2);
		root.left.left = new BinaryTree(1);
		root.left.left.left = new BinaryTree(0);
		root.left.right = new BinaryTree(4);
		root.left.right.left = new BinaryTree(3);
		root.left.right.right = new BinaryTree(5);
		
		root.right = new BinaryTree(11);
		root.right.left = new BinaryTree(7);
		root.right.right = new BinaryTree(9);
		root.right.right.left = new BinaryTree(8);
		root.right.right.right = new BinaryTree(10);
		
//		preOrderTraversal(root);System.out.println(stringBuilder);
		
//		inOrderTraversal(root);System.out.println(stringBuilder);
		
//		postOrderTraversal(root);System.out.println(stringBuilder);
		inOrderTraversal(root);System.out.println(stringBuilder);
		reversal(root);
		stringBuilder = new StringBuilder();
		inOrderTraversal(root);System.out.println(stringBuilder);
	}
}