MathDB
Fill the table with T,M,O

Source: 2021 Thailand Online MO P10 (Mock TMO contest)

April 6, 2021
combinatoricsThailand online MOdesi chudayio physicsknight muth mrnejrha

Problem Statement

Each cell of the board with 20212021 rows and 20222022 columns contains exactly one of the three letters TT, MM, and OO in a way that satisfies each of the following conditions:
[*] In total, each letter appears exactly 2021×6742021\times 674 of times on the board. [*] There are no two squares that share a common side and contain the same letter. [*] Any 2×22\times 2 square contains all three letters TT, MM, and OO.
Prove that each letter TT, MM, and OO appears exactly 674674 times on every row.