226. Invert Binary Tree

226. Invert Binary Tree

1. 问题

Invert a binary tree.

Example:

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

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

轶事：牛逼的工程师都这样吗？??

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

2. 解法

• 思路：通过递归实现将左右子树翻转。
• C代码如下：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

/*递归将左右子树交换，从而完成整棵树的翻转*/
struct TreeNode* invertTree(struct TreeNode* root){
    if(NULL == root){
        return NULL;
    }

    struct TreeNode* tmp = root->right;
    root->right = root->left;
    root->left  = tmp;

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

    return root;
}