A board $2025 \times 2025$ is filled with the numbers $1, 2, \ldots, 2025$, each appearing exactly $2025$ times. Show that there is a row or column with at least $45$ distinct numbers.
Source: Bulgaria MO Regional round 2024, 11.4
Tags: combinatorics
A board $2025 \times 2025$ is filled with the numbers $1, 2, \ldots, 2025$, each appearing exactly $2025$ times. Show that there is a row or column with at least $45$ distinct numbers.