Leetcode 226:invert Binary Tree

Topic:

Invert a binary tree.

     4   /     2     7/\   /1   3 6   9

To

     4   /     7     2/\   /9   6 3   1

Trivia:
This problem is inspired by this original tweets by Max Howell:

google:90% of our engineers with the software you wrote (Homebrew), but can ' t invert a binary tree on a whiteboard so Fuck off.

Ideas:

Permutation, recursive, left and right sub-tree substitution

Code:

/*** Definition for a binary tree node. * public class TreeNode {* int val; * TreeNode left; * TreeNode RI Ght * TreeNode (int x) {val = x;} }*/ Public classSolution { PublicTreeNode inverttree (TreeNode root) {if(Root = =NULL)             returnRoot; Else {            if(root.left!=NULL&& root.right!=NULL) {TreeNode temp; Temp=Root.left; Root.left=Root.right; Root.right=temp;                Inverttree (Root.left);            Inverttree (Root.right); } Else if(Root.left = =NULL&& Root.right! =NULL) {Root.left=Root.right; Root.right=NULL;            Inverttree (Root.left); } Else if(Root.left! =NULL&& Root.right = =NULL) {Root.right=Root.left; Root.left=NULL;            Inverttree (Root.right); } Else {                returnRoot; }        }        returnRoot; }}

Leetcode 226:invert Binary Tree