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Putnam
2020 Putnam
B2
B2
Part of
2020 Putnam
Problems
(1)
Putnam 2020 B2
Source: 81st William Lowell Putnam Competition
2/22/2021
Let
k
k
k
and
n
n
n
be integers with
1
≤
k
<
n
1\leq k<n
1
≤
k
<
n
. Alice and Bob play a game with
k
k
k
pegs in a line of
n
n
n
holes. At the beginning of the game, the pegs occupy the
k
k
k
leftmost holes. A legal move consists of moving a single peg to any vacant hole that is further to the right. The players alternate moves, with Alice playing first. The game ends when the pegs are in the
k
k
k
rightmost holes, so whoever is next to play cannot move and therefore loses. For what values of
n
n
n
and
k
k
k
does Alice have a winning strategy?
Putnam
Putnam 2020