InvertBinaryTree.java

/**
 * 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 temp = root.left;
        
        root.left = invertTree(root.right);
        root.right = invertTree(temp);
        
        return root;
    }
}