Fastest method to generate big random string with lower Latin letters

Question

I\'m trying to solve this problem from Timus Online Judge. To solve this problem you need generate a sequence of 1 000 000 lowercase Latin letters and write it to stdin in

Answer 1

Generate and write in chunks that are a larger power of 2 in size.

Maybe use a string or array of the 26 lower-case letters and randomly pick then instead of generating chars.