---
tags: leetcode
---

# [226. Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)
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# My Solution
## The Key Idea for Solving This Coding Question
## C++ Code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if (root == nullptr) {
            return nullptr;
        }
        
        TreeNode *left = invertTree(root->left);
        TreeNode *right = invertTree(root->right);
        
        root->left = right;
        root->right = left;
        
        return root;
    }
};

## Time Complexity
$O(n)$
$n$ is the number of nodes in the binary tree referred by `root`.
## Space Complexity
$O(H)$
$H$ is the height of the binary tree referred by `root`.
# Miscellane
<!--
# Test Cases

[4,2,7,1,3,6,9]

[2,1,3]

[]

[1,2,null,3,null,4,null,5]

-->