描述

操作给定的二叉树，将其变换为源二叉树的镜像。
源二叉树

            8
           /  \
          6   10
         / \  / \
        5  7 9 11
        镜像二叉树
            8
           /  \
          10   6
         / \  / \
        11 9 7  5

代码

1. 递归

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
*/

public class Solution {
    public void Mirror(TreeNode root) {
        if (root == null) {
            return;
        }
        
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        
        Mirror(root.left);
        Mirror(root.right);
    }
}

2. 非递归用栈

import java.util.Stack;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/

public class Solution {
    public void Mirror(TreeNode root) {
        if (root == null) {
            return;
        }
        
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        
        while (!stack.isEmpty()) {
            TreeNode node = stack.pop();
            
            TreeNode temp = node.left;
            node.left = node.right;
            node.right = temp;
            
            if (node.left != null) {
                stack.push(node.left);
            }
            if (node.right != null) {
                stack.push(node.right);
            }
        }
    }
}