Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3

But the following [1,2,2,null,3,null,3] is not:

    1
   / \
  2   2
   \   \
   3    3


Solution:
class Solution {
public:
        bool recursiveJudgeSym(TreeNode* left, TreeNode* right)
        {
                if((!left && right) || (left && !right)) return false;
                else if(!left && !right) return true;
                else
                {
                        if(left->val == right->val)
                        {
                                return recursiveJudgeSym(left->left, right->right) &&
                                recursiveJudgeSym(left->right, right->left);
                        }
                        else return false;
                }
        }
    
        bool isSymmetric(TreeNode* root) 
        {
                if(root)
                {
                        return recursiveJudgeSym(root->left, root->right);
                }
                else return true;
        }
};

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