text: #include <stdio.h>
  #include <stdlib.h>
  
  /*
   * AC
   * https://leetcode-cn.com/submissions/detail/75251482/
   *
   */
  
  /**
   * Definition for a binary tree node.
   * struct TreeNode {
   *     int val;
   *     struct TreeNode *left;
   *     struct TreeNode *right;
   * };
   */
  bool isSymmetric_node(struct TreeNode* node1,struct TreeNode* node2){
      if(node1 == NULL || node2 == NULL) {
          if(node1 == node2) {
              return true;
          } else {
              return false;
          }
      }
      if(node1->val == node2->val) {
          return (isSymmetric_node(node1->left,node2->right) &&
                  isSymmetric_node(node2->left,node1->right));
      } else {
          return false;
      }
  }
  
  bool isSymmetric(struct TreeNode* root){
      if(root == NULL) {
          return true;
      }
      return (isSymmetric_node(root->left,root->right));
  }
  
  int main()
  {
      printf("Hello world!\n");
      return 0;
  }
  