对称的二叉树

#include <iostream>
using namespace std;

struct tree
{
    double data;
    struct tree *left,*right;
    tree(int d=0):data(d)
    {
        left=right=nullptr;
    }
};
class Solution
{
    public:
        void create(tree *&root);
        void pre_order(const tree *root);
        bool is_symmetric();
        bool is_symmetric(const tree *r1,const tree *r2); 
        tree *root;    
};
void Solution::create(tree *&root)
{
    double x;
    cin>>x;
    if(x==0)
        root=nullptr;
    else
    {
        root=new tree();
        root->data=x;
        create(root->left);
        create(root->right);
    }
}
void Solution::pre_order(const tree *root)
{
    if(root)
    {
        cout<<root->data<<endl;
        pre_order(root->left);
        pre_order(root->right);
    }
}
bool Solution::is_symmetric()
{
    return is_symmetric(root,root);
}
bool Solution::is_symmetric(const tree *r1,const tree *r2)
{
    if(!r1&&!r2)
        return true;
    if(!r1||!r2)
        return false;
        
    if(r1->data!=r2->data)
        return false;
    return is_symmetric(r1->left,r2->right)&&is_symmetric(r1->right,r2->left);
}
int main()
{
    Solution s;
    s.create(s.root);
    cout<<boolalpha<<s.is_symmetric()<<endl;
    
    return 0;
}