226. Invert Binary Tree

Posted 2022-08-03 wx62ea2466cca9a

Invert a binary tree.

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

to

     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 fuck off.

/**
 * Definition for a binary tree node.
 * public class TreeNode 
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x)  val = x; 
 * 
 */
public class Solution 
    public TreeNode invertTree(TreeNode root) 
        if (root == null) 
            return null;
        

        TreeNode tempNode = root.left;
        root.left = root.right;
        root.right = tempNode;

        invertTree(root.left);
        invertTree(root.right);

        return root;
    

/**
 * Definition for a binary tree node.
 * public class TreeNode 
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x)  val = x; 
 * 
 */
public class Solution 
    public TreeNode invertTree(TreeNode root) 
        if(root == null)
            return root;
        TreeNode curr = new TreeNode(root.val);
        curr.right = invertTree(root.left);
        curr.left  = invertTree(root.right);
        return curr;