LeetCode 226. 翻转二叉树

翻转一棵二叉树。

递归每个节点交换其两个孩子即可：

/**
 * 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 (nullptr == root) {
            return nullptr;
        }

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

        return root;
    }
};