struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};

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