一棵二叉树是否为另一棵二叉树的子树

#include <iostream>
using namespace std;

struct node{
int data;
node *left;
node *right;

node(const int &x, node *l = NULL, node *r = NULL){
data = x;
left = l;
right = r;
}
~node(){}
};

bool treecore(node *tree1, node *tree2){
bool flag = false;
if (tree2 == NULL)
return true;
if (tree1 == NULL)
return false;
if (tree1->data == tree2->data){
return treecore(tree1->left, tree2->left) && treecore(tree1->right, tree2->right);  //两种写法是一样的，程序在判断&&前一个条件为false时会直接返回false
//flag = treecore(tree1->left, tree2->left);
//if (!flag)
//  return false;
//flag = treecore(tree1->right, tree2->right);
//if (!flag)
//  return false;
//return true;
}
return false;
}

bool subtree(node *tree1, node *tree2){
bool flag = treecore(tree1, tree2);

if (!flag && tree1 != NULL)
flag = subtree(tree1->left, tree2);

if (!flag && tree1 != NULL)
flag = subtree(tree1->right, tree2);

return flag;
}

int main(){
node *tmp;

node *tree1 = new node(8);
tmp = new node(8);
tree1->left = tmp;
tmp = new node(7);
tree1->right = tmp;
tmp = new node(9);
tree1->left->left = tmp;
tmp =  new node(2);
tree1->left->right = tmp;
tmp = new node(4);
tree1->left->right->left = tmp;
tmp = new node(7);
tree1->left->right->right = tmp;

node *tree2 = new node(8);
tmp = new node(9);
tree2->left = tmp;
tmp = new node(7);  //改成7则不是子树
tree2->right = tmp;

bool isSubtree = subtree(tree1, tree2);
cout << isSubtree <<endl;

int ttt = 0;

return 0;
}