Symmetric Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isConsistent(TreeNode *leftNode, TreeNode *rightNode) {
        if(leftNode == NULL && rightNode == NULL)
            return true;
        if(leftNode == NULL || rightNode == NULL)
            return false;
        return leftNode->val == rightNode->val && isConsistent(leftNode->left, rightNode->right) 
            && isConsistent(leftNode->right, rightNode->left);
    }
    bool isSymmetric(TreeNode* root) {
        if(root == NULL)
        return true;
        return isConsistent(root->left, root->right);
    }
};