bst_count_classic.cpp

long long bst_count_classic(int n)
{
   if (n <= 1) return 1;
    
   std::vector<long long> memo(n+1, 0);
   memo[0] = memo[1] = 1;
   for (int k = 2; k <= n; ++k)
      for (int i = 0; i < k; ++i)
         memo[k] += memo[i] * memo[k-i-1];
   return memo.back();
}