//写树的时候最好用模拟+递归;
#include <stdbool.h>
bool isMirror(struct TreeNode* left,struct TreeNode* right)
{
    if(left==NULL&&right==NULL) return true;
    if(left==NULL||right==NULL) return false;
    if(left->val!=right->val) return false;
    return isMirror(left->left,right->right)&&isMirror(left->right,right->left);
}
bool isSymmetrical(struct TreeNode* root ) {
    if(!root) return true;
    return isMirror(root->left,root->right);
}