Leetcode 156 Solution

This article provides solution to leetcode question 156 (binary-tree-upside-down)
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https://leetcode.com/problems/binary-tree-upside-down

Solution

/**
 * 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* upsideDownBinaryTree(TreeNode* root) {
        if (root == NULL || root->left == NULL)
            return root;



        auto left_child = root->left;
        auto right_child = root->right;



        auto left_tree = upsideDownBinaryTree(root->left);
        auto right_tree = upsideDownBinaryTree(root->right);



        left_child->right = root;
        left_child->left = right_tree;



        root->left = root->right = NULL;



        return left_tree;
    }
};