LeetCode 156. 上下翻转二叉树

LeetCode 156. 上下翻转二叉树

思路：

递归，递归最主要的就是处理好一般情况。

代码：

/**
 * 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* upsideDownBinaryTree(TreeNode* root) {
        if(!root || !root->left) return root;
        auto l = root->left;
        auto r = root->right;
        root->left = nullptr;
        root->right = nullptr;
        auto res = upsideDownBinaryTree(l);
        l->left = r;
        l->right = root;
        return res;
    }
};