牛客网刷题(JAVA) 20：二叉树的镜像

难度系数 ⭐⭐难在思路

时间限制 C/C++ 1秒，其他语言2秒 空间限制：C/C++ 32M，其他语言64M

题目内容 操作给定的二叉树，将其变换为源二叉树的镜像。

输入描述 

二叉树的镜像定义：源二叉树 
    	    8
    	   /  \
    	  6   10
    	 / \  / \
    	5  7 9 11
    	镜像二叉树
    	    8
    	   /  \
    	  10   6
    	 / \  / \
    	11 9 7  5

思路 二叉树的镜像，其实就是把二叉树每个节点的左右孩子换一下，所以一边遍历一边换就可以了。

package nowcoder;

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

public class No21 {
    public static class Node{
        public int value;
        public Node left;
        public Node right;

        public Node(int value){
            this.value = value;
        }
    }

    public static void Mirror(Node head){
        if (head == null) return;

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

        while (!queue.isEmpty()){
            Node flag = queue.poll();
            if (flag.left != null) queue.offer(flag.left);
            if (flag.right != null) queue.offer(flag.right);

            Node f = flag.left;
            flag.left = flag.right;
            flag.right = f;
        }
    }


    public static void printTree(Node head) {
        System.out.println("Binary Tree:");
        printInOrder(head, 0, "H", 17);
        System.out.println();
    }

    public static void printInOrder(Node head, int height, String to, int len) {
        if (head == null) {
            return;
        }
        printInOrder(head.right, height + 1, "v", len);
        String val = to + head.value + to;
        int lenM = val.length();
        int lenL = (len - lenM) / 2;
        int lenR = len - lenM - lenL;
        val = getSpace(lenL) + val + getSpace(lenR);
        System.out.println(getSpace(height * len) + val);
        printInOrder(head.left, height + 1, "^", len);
    }

    public static String getSpace(int num) {
        String space = " ";
        StringBuffer buf = new StringBuffer("");
        for (int i = 0; i < num; i++) {
            buf.append(space);
        }
        return buf.toString();
    }

    public static void main(String[] args){
        Node head = new Node(8);
        head.left = new Node(6);
        head.right = new Node(10);
        head.left.left = new Node(5);
        head.left.right = new Node(7);
        head.right.left = new Node(9);
        head.right.right = new Node(11);

        printTree(head);
        Mirror(head);
        printTree(head);
    }
}