Given n (at most 9, so every number is a single digit), return n centred rows where row i counts up from 1 to i and back down to 1 — for example "12321" for i = 3. Every row is a palindromePalindromeA sequence that reads the same forwards and backwards, such as 12321., and the rows grow by two characters each time, which is why they stack into a pyramid once n − i leading spaces are added. The second solution uses the palindrome property directly: build the rising half once and mirror it.