LeeCode-Invert Binary Tree

Invert a binary tree.

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

to

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

 /**
  * 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)
         {
         TreeNode temp  = root.left;
         root.left = root.right;
         root.right = temp;  

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

         return root;
         }
         return null;
     }
 }