MathDB
Polynomial dividing Points

Source: All Russian Olympiad 2015 11.4

December 11, 2015
algebrapolynomialcombinatorics

Problem Statement

You are given NN such that n3 n \ge 3. We call a set of NN points on a plane acceptable if their abscissae are unique, and each of the points is coloured either red or blue. Let's say that a polynomial P(x)P(x) divides a set of acceptable points either if there are no red dots above the graph of P(x)P(x), and below, there are no blue dots, or if there are no blue dots above the graph of P(x)P(x) and there are no red dots below. Keep in mind, dots of both colors can be present on the graph of P(x)P(x) itself. For what least value of k is an arbitrary set of NN points divisible by a polynomial of degree kk?