100.Same Tree

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<TreeNode*> 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();
    }
};