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IMO 2021 — Complete Shortlist Question 16

IMO Shortlist · IMO 2021 — Complete Shortlist

Question 16

Determine the largest $N$ for which there exists a table $T$ of integers with $N$ rows and 100 columns that has the following properties:
(i) Every row contains the numbers $1,2, \ldots, 100$ in some order.
(ii) For any two distinct rows $r$ and $s$, there is a column $c$ such that $|T(r, c)-T(s, c)| \geqslant 2$.

Here $T(r, c)$ means the number at the intersection of the row $r$ and the column $c$.