【剑指offer】二叉树的镜像

public class  {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public (int val) {
        this.val = val;
    }
}

public void Mirror(TreeNode root) {
    if (root == null)
        return;
    else if (root.left == null && root.right == null)
        return;

    TreeNode tmp = root.left;
    root.left = root.right;
    root.right = tmp;

    Mirror(root.left);
    Mirror(root.right);
}