LeetCode-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){
            return null;
        }
        if(root.left==null && root.right==null){
            return root;
        }
        TreeNode temp=root.left;
        root.left=invertTree(root.right);
        root.right=invertTree(temp);
        return root;
    }
}