226.InvertBinaryTree_Kris.java

// Source : https://leetcode.com/problems/invert-binary-tree/
// Author : Kris
// Date : 2020-08-28

/***************************************************************************************************** 
 *
 * 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() {}
 * TreeNode(int val) { this.val = val; }
 * TreeNode(int val, TreeNode left, TreeNode right) {
 * this.val = val;
 * this.left = left;
 * this.right = right;
 * }
 * }
 */
classSolution {
publicTreeNodeinvertTree(TreeNoderoot) {
if (root == null) {
returnnull;
 }

TreeNodeleft = invertTree(root.left);
TreeNoderight = invertTree(root.right);

root.left = right;
root.right = left;

returnroot;
 }
}