leetcode Same Tree

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.

一般树的问题，用递归方式比较容易解决：

if(p==NULL && q==NULL) return true;
	else if(p==NULL)  return false;
	else if(q==NULL)  return false;
   return (p->val==q->val &&isSameTree(p->left,q->left)&& isSameTree(p->right,q->right));

尝试用了非递归算法，自己vs里创建两棵树比较，返回正确。这里一直报错。