/**

 * Definition of TreeNode:

 * public class TreeNode {

 *     public int val;

 *     public TreeNode left, right;

 *     public TreeNode(int val) {

 *         this.val = val;

 *         this.left = this.right = null;

 *     }

 * }

 */

public class Solution {

    /**

     * @param root: a TreeNode, the root of the binary tree

     * @return: nothing

     */

    // method 1: recursion

    // 注意交换的是node，不是int value

    public void invertBinaryTree(TreeNode root) {

        if (root == null)

            return;

        TreeNode temp = root.left;

        root.left = root.right;

        root.right = temp;

        invertBinaryTree(root.left);

        invertBinaryTree(root.right);

    }

}