class Solution {public:    bool isSameTree(TreeNode *p, TreeNode *q) {        if (!p && !q) return true;        if ((p && !q) || (!p && q) || (p->val != q->val)) return false;        return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);    }};

class Solution {public:    bool isSameTree(TreeNode* p, TreeNode* q) {        stack
    
      s1, s2;        if (p) s1.push(p);        if (q) s2.push(q);        while (!s1.empty() && !s2.empty()) {            TreeNode *t1 = s1.top(); s1.pop();            TreeNode *t2 = s2.top(); s2.pop();            if (t1->val != t2->val) return false;            if (t1->left) s1.push(t1->left);            if (t2->left) s2.push(t2->left);            if (s1.size() != s2.size()) return false;            if (t1->right) s1.push(t1->right);            if (t2->right) s2.push(t2->right);            if (s1.size() != s2.size()) return false;        }        return s1.size() == s2.size();    }};