Using your Head is Permitted

February 2017 riddle

SPECIAL ANNOUNCEMENT: Next month marks Using your Head is Permitted's ten year anniversary. To celebrate, I am inviting readers to send riddles to appear as the site's special anniversary riddle. (Hint: riddles that feature the number '10' will be especially appreciated.)

Readers are welcomed to send in multiple suggestions. Please send riddles in together with their solutions.

Looking forward to hearing your ideas!

This month's riddle comes from Jim Boyce. (Thanks, Jim!) It is a continuation of last month's riddle, and picks up where that other riddle left off.

Spoiler alert: The following description contains hints regarding the solution of the January 2017 riddle. If you still mean to tackle that other riddle, you may want to hold on before you continue to this one.

In the previous riddle we asked if a particular task can be performed in O(n) time. This month, Jim asks if the same task can be performed in o(n) time, which is to say, a time which is significantly better (i.e., by more than a constant multiplicative factor) than O(n).

As always, you are required to prove your answer.

List of solvers:

Oscar Volpatti (30 January 18:59)
Tianyi Zhang (1 February 16:28)
JJ Rabeyrin (5 February 00:06)
Lin Jin (12 February 22:35)

Elegant and original solutions can be submitted to the puzzlemaster at Names of solvers will be posted on this page. Notify if you don't want your name to be mentioned.

The solution will be published at the end of the month.


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