MathDB
Problems
Contests
National and Regional Contests
China Contests
China Team Selection Test
2024 China Team Selection Test
14
14
Part of
2024 China Team Selection Test
Problems
(1)
n-good sets
Source: 2024 CTST P14
3/24/2024
For a positive integer
n
n
n
and a subset
S
S
S
of
{
1
,
2
,
…
,
n
}
\{1, 2, \dots, n\}
{
1
,
2
,
…
,
n
}
, let
S
S
S
be "
n
n
n
-good" if and only if for any
x
x
x
,
y
∈
S
y\in S
y
∈
S
(allowed to be same), if
x
+
y
≤
n
x+y\leq n
x
+
y
≤
n
, then
x
+
y
∈
S
x+y\in S
x
+
y
∈
S
. Let
r
n
r_n
r
n
be the smallest real number such that for any positive integer
m
≤
n
m\leq n
m
≤
n
, there is always a
m
m
m
-element "
n
n
n
-good" set, so that the sum of its elements is not more than
m
⋅
r
n
m\cdot r_n
m
⋅
r
n
. Prove that there exists a real number
α
\alpha
α
such that for any positive integer
n
n
n
,
∣
r
n
−
α
n
∣
≤
2024.
|r_n-\alpha n|\leq 2024.
∣
r
n
−
α
n
∣
≤
2024.
combinatorics