MathDB
Painting a fence with 100 colors

Source: 2021 Thailand Online MO P1 (Mock TMO contest)

April 6, 2021
combinatoricsThailand online MO

Problem Statement

There is a fence that consists of nn planks arranged in a line. Each plank is painted with one of the available 100100 colors. Suppose that for any two distinct colors ii and jj, there is a plank with color ii located to the left of a (not necessarily adjacent) plank with color jj. Determine the minimum possible value of nn.