// 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 InvertBinaryTree {
    public TreeNode invertTree(TreeNode root) {
        if(root == null) {
            return root;
        }
        
        TreeNode temp = root.left;
        root.left = invertTree(root.right);
        root.right = invertTree(temp);
        
        return root;
    }
}