二叉树的镜像（剑指offer_27）

public class Solution {
    public void Mirror(TreeNode root) {
        if(root == null)
            return;
        swap(root);
        Mirror(root.left);
        Mirror(root.right);
    }
    
    public void swap(TreeNode root)
    {
        TreeNode t = root.left;
        root.left = root.right;
        root.right = t;
    }
}