• 先枚举

	string s; queue<string>q;
	vector<string> v;
	for (int i = 1; i <= 9; i++)
		q.push(to_string(i));
	while (!q.empty()) {
		string t = q.front(); q.pop();
		int tmp = t.size();
		if (tmp >= 10)continue;
		if (t.size() > 1)v.push_back(t);
		if (t[tmp - 1] - 1 >= '0')q.push(t + char(t[tmp - 1] - 1));
		if (t[tmp - 1] + 1 <= '9')q.push(t + char(t[tmp - 1] + 1));
	}

• 再搜索

	cin >> T;
	while (T--) {
		cin >> l >> r;
		string sr = to_string(r), sl = to_string(l);
		int cnt = 0;
		for (int i = 0; i < v.size() && cmp(v[i], sr); i++) {
			if (!cmp(v[i], sl) || sl == v[i])
				cnt++;
		}
		cout << cnt << endl;
	}