226. Invert Binary Tree

https://leetcode.com/problems/invert-binary-tree

Problem

Invert a binary tree.

Example:

Input:

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

Output:

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

Trivia: This problem was inspired by this original tweet by Max Howell:

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.

Solution

/**
 * 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* invertTree(TreeNode* root) {
        invertTreeHelper(root);
        return root;
    }
    void invertTreeHelper(TreeNode* root) {
        if (root == nullptr) return;
        auto *temp = root->left;
        root->left = root->right;
        root->right = temp;
        invertTreeHelper(root->left);
        invertTreeHelper(root->right);
    }
};

• #tree

• #dfs