226.invert-binary-tree.java

/*
 * @lc app=leetcode id=226 lang=java
 *
 * [226] Invert Binary Tree
 *
 * https://leetcode.com/problems/invert-binary-tree/description/
 *
 * algorithms
 * Easy (59.32%)
 * Likes:    1976
 * Dislikes: 35
 * Total Accepted:    358K
 * Total Submissions: 601.9K
 * Testcase Example:  '[4,2,7,1,3,6,9]'
 *
 * 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.
 *
 */
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
  public TreeNode invertTree(TreeNode root) {
    if (root == null) {
      return null;
    }
    TreeNode left = invertTree(root.right);
    TreeNode right = invertTree(root.left);
    root.left = left;
    root.right = right;
    return root;
  }
}