MathDB
Santa Claus game, present behind 1 of 100 doors

Source: 2020 Dürer Math Competition Finals Day2 E7 https://artofproblemsolving.com/community/c1622639_2020_

January 7, 2022
combinatoricsgame

Problem Statement

Santa Claus plays a guessing game with Marvin before giving him his present. He hides the present behind one of 100100 doors, numbered from 11 to 100100. Marvin can point at a door, and then Santa Claus will reply with one of the following words:
\bullet "hot" if the present lies behind the guessed door,
\bullet "warm" if the guess is not exact but the number of the guessed door differs from that of the present’s door by at most 55,
\bullet "cold" if the numbers of the two doors differ by more than 55.
At least how many such guesses does Marvin need, so that he can be certain about where his present is?
Marvin does not necessarily need to make a "hot" guess, just to know the correct door with 100%100\% certainty.