题目：
Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
代码如下：
bool isSameTree(TreeNode *p, TreeNode *q) {
if(p==NULL&&q==NULL)return true;
if(p==NULL||q==NULL)return false;
if(p->val!=q->val)
{
return false;
}
else
{
return isSameTree(p->left, q->left)&&isSameTree(p->right, q->right);
}
}