226. Invert Binary Tree 226. Invert Binary Tree LeetCode Invert Binary Tree Invert a binary tree.

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

to

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

Trivia: This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

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本题要把二叉树翻转，看题目中的例子，也就是交换树的左右子树，然后递归的交换就好了。简单题，完整代码如下：

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

本代码提交AC，用时3MS。