Labelling points
Source: 2017 SDMO High School Problem 5
November 8, 2017
Problem Statement
There are dots on the plane such that no three dots are collinear. Each dot is assigned a or a . Each pair of dots is connected by a line segment. If the endpoints of a line segment are two dots with the same number, then the segment is assigned a . Otherwise, the segment is assigned a . Find all such that it is possible to assign 's and 's to the dots in a way that the corresponding line segments are assigned equally many 's as 's.