請實現一個函數，用來判斷一顆二叉樹是不是對稱的。注意，如果一個二叉樹同此二叉樹的鏡像是同樣的，定義其為對稱的。

遞歸遍歷判斷

/*public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class Solution {    boolean isSymmetrical(TreeNode PRoot){        if(pRoot == null)return true;         return judge(pRoot.left , pRoot.right) ;     }    private boolean judge(TreeNode left , TreeNode right){        if(left == null && right != null)return false ;         if(left != null && right == null)return false ;         if(left != null && right != null && left.val != right.val)return false ;         if(left == null && right == null)return true ;         if(!judge(left.left , right.right))return false ;         if(!judge(left.right , right.left))return false ;         return true  ;     }}