操作给定的二叉树，将其变换为源二叉树的镜像。

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

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

    }

}
*/
public class Solution {
    public void Mirror(TreeNode root) {
        if(root == null) return;
        TreeNode left = root.left;
        TreeNode right = root.right;
        
        root.left = right;
        root.right = left;
        
        if(root.left != null){
            Mirror(root.left);
        }
        if(root.right != null){
            Mirror(root.right);
        }
    }
    
}