/// https://leetcode.com/problems/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 helper(TreeNode *leftTree,TreeNode* rightTree){
        if(leftTree==NULL && rightTree!=NULL) return false;
        if(leftTree!=NULL && rightTree==NULL) return false;
        if(leftTree==NULL && rightTree==NULL) return true;
        
        if(leftTree->val != rightTree->val) return false;
        
        
        return helper(leftTree->left,rightTree->right) &&
               helper(leftTree->right,rightTree->left);
    }
    bool isSymmetric(TreeNode* root) {
        if(root==NULL) return true;
        
        return helper(root->left,root->right);
    
    }
};