The program for a given polygonal line L in the plane (`obstacle') and points A,B outside L constructs another polygonal line joining A to B and disjoint with L. The program can easily be modified to the case when the obstacle is a linear tree in the plane. The program does not use any complex algorithms. It builds a polygonal line that has O(n) vertexes in O(n^2) time, where n is the number of vertexes in given polygonal line.
This program was prepared in frame of the course `Discrete structures and lgorithms in topology' in Moscow Institute of Physics and Technology [hyperref]. The program illustrates the fact that a tree does not separate the plane (or a surface), which is the main ingredient for the Euler inequality.
https://github.com/mmilunovic/Shortest-path-among-polygons this program builds a shortest path between two point, avoiding obstacles that are a set of disjoined simple polygons. It solves more difficult problem in nearly equal time, but it uses more complicated algorithms based on visibility graphs.