leetcode Revert Binary Tree

homebrew的作者面试google,面试官要求他手写一个反转一个二叉树的功能。最后却没写出来，于是有了下面的新闻：

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.

Invert a binary tree.

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

to

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

这个题我在书上看到过，我认为上面的图解比较清楚，就放了上来。

大体思路：一层一层反转左右节点，直到下到叶子



/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
struct TreeNode* invertTree(struct TreeNode* root) {
if(root == NULL)
return ;
if(root->left == NULL && root->right == NULL)
return root;

struct TreeNode* temp;

temp=root->left;
root->left = root->right;
root->right = temp;

if(root->left)
invertTree(root->left);
if(root->right)
invertTree(root->right);

return root;

}