翻轉一棵二叉樹。 示例： 輸入：

     4
   /   \
  2     7
 / \   / \
1   3 6   9

輸出：

     4
   /   \
  7     2
 / \   / \
9   6 3   1

這個題的思路就是兩數交換的思路，只是需要遍歷每一個節點，然後把每個節點的左右兩個節點都交換。既可以用遞迴，也可以用迭代，都是很簡單的思想。和之前一樣用c++寫遞迴，用python3寫迭代，迭代還是使用佇列來進行遍歷（層次遍歷）。 C++原始碼：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 

class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if (root==NULL)
            return NULL;
        TreeNode *tmp = root->left;
        root->left = invertTree(root->right);
        root->right = invertTree(tmp);
        return root;
    }
};

python3原始碼：

# Definition for a binary tree node.
 

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def invertTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if root==None:
            return None
        q =
 
 [root]
        while len(q):
            now = q.pop(0)
            tmp = now.left
            now.left = now.right
            now.right = tmp
            if now.left!=None: 
                q.append(now.left)
            if now.right!=None:
                q.append(now.right)
        return root