// Time:  O(n)
// Space: O(h), h is height of binary tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        if (!p && !q) {
            return true;
        }
        return p && q && p->val == q->val &&
               isSameTree(p->left, q->left) &&
               isSameTree(p->right, q->right);
    }
};