反转二叉树 打印二叉树

代码：

package com.qhong;


import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

public class Main {
    public static void main(String[] args)   {
        TreeNode root =new TreeNode(0);
        TreeNode left=new TreeNode(1);
        TreeNode right=new TreeNode(2);
        TreeNode left2=new TreeNode(3);
        TreeNode right2=new TreeNode(4);
        TreeNode left3=new TreeNode(5);
        TreeNode right3=new TreeNode(6);
       left.left=left2;
       left.right=right2;
       right.left=left3;
       //right.right=right3;
       root.left=left;
       root.right=right;

       Print.PrintTreeNode(root);
       Solution.invertTree(root);
        Print.PrintTreeNode(root);
    }
}

class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;

      TreeNode(int x) {
          val = x;
      }
  }


class Solution {
    public static TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }
        if (root.left != null) {
            invertTree(root.left);
        }
        if (root.right != null) {
            invertTree(root.right);
        }
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        return root;
    }
}


class Print{
    //打印TreeNode
    public static void PrintTreeNode(TreeNode root){
        ArrayList arrayList=PrintFromTopToBottom(root);
        printTree(arrayList,arrayList.size());
    }
    //转换TreeNode为ArrayList
    private static ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {

        ArrayList<Integer> list = new ArrayList();
        if(root == null)
            return list;

        Queue<TreeNode> queue = new LinkedList();
        queue.offer(root);

        while(!queue.isEmpty()){
            TreeNode treeNode = queue.poll();
            list.add(treeNode.val);
            if(treeNode.left != null)
                queue.offer(treeNode.left);
            if(treeNode.right != null)
                queue.offer(treeNode.right);
        }

        return list;
    }

    //以树形打印ArrayList
    private static void printTree(ArrayList array,int len){

        int layers = (int)Math.floor(Math.log((double)len)/Math.log((double)2))+1;  //树的层数
        int maxWidth = (int)Math.pow(2,layers)-1;  //树的最大宽度
        int endSpacing = maxWidth;
        int spacing;
        int numberOfThisLayer;
        for(int i=1;i<=layers;i++){  //从第一层开始，逐层打印
            endSpacing = endSpacing/2;  //每层打印之前需要打印的空格数
            spacing = 2*endSpacing+1;  //元素之间应该打印的空格数
            numberOfThisLayer = (int)Math.pow(2, i-1);  //该层要打印的元素总数

            int j;
            for(j=0;j<endSpacing;j++){
                System.out.print("  ");
            }

            int beginIndex = (int)Math.pow(2,i-1)-1;  //该层第一个元素对应的数组下标
            for(j=1;j<=numberOfThisLayer;j++){
                System.out.print(array.get(beginIndex++)+"");
                for(int k=0;k<spacing;k++){  //打印元素之间的空格
                    System.out.print("  ");
                }
                if(beginIndex == len){  //已打印到最后一个元素
                    break;
                }
            }

            System.out.println();
        }
        System.out.println();
    }

}

      0              
  1      2      
3  4  5  

      0              
  2      1      
5  4  3  

解决方法二：使用栈来模拟递归过程

class Solution {
    /**
     * 翻转二叉树
     * @param root 二叉树的根
     * @return
     */
    public  static  TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return root;
        }
        Stack<TreeNode> stack = new Stack<TreeNode>();
        stack.push(root);
        while (!stack.isEmpty()) {
            TreeNode node = stack.peek();
            stack.pop();
            if (node.left != null) {
                stack.push(node.left);
            }
            if (node.right != null) {
                stack.push(node.right);
            }
            for(int i=0;i<stack.size();i++){
                System.out.println(stack.elementAt(i).val);
            }
            System.out.println("=============");
            TreeNode temp = node.left;
            node.left = node.right;
            node.right = temp;
        }
        return root;
    }
}

0              
  1      2      
3  4  5  6  

1
2
=============
1
5
6
=============
1
5
=============
1
=============
3
4
=============
3
=============
=============
      0              
  2      1      
6  5  4  3  

https://my.oschina.net/Tsybius2014/blog/614514

http://www.cnblogs.com/wintersoft/p/4676124.html

https://www.nowcoder.com/questionTerminal/bcffd7e8a0d4402c99773bed98690bb7