Draw a map and let it be colored – Four color theorem demo
Draw a map and let it be colored – Four color theorem demo launched on April 15, 2016 with 48 votes, #1,655 of 4,301 launches that month and more than 90% of that year's launches. The site was still online in September 2026, 10 years on.
In plain words
This interactive tool lets users draw lines on a canvas to create map regions, then applies an automated coloring algorithm based on the four color theorem. After drawing, users click solve and the application colors adjacent regions with different colors, using backtracking techniques to find valid solutions within a 10-second limit. Built with ProcessingJS, it demonstrates graph coloring principles through a hands-on drawing interface.
written from the facts on this page · September 2026
From the sources
Draw lines on the canvas and after you've finished, click solve to color the map. Note: Backtracking may take some time and may not always find a solution in time (10s max). The coloring and canvas handling is powered by ProcessingJS . The steps for solving a graph are the following: It's necessary to have clear borders for finding distinct areas, and also for the examination of neighbor. As you can see, the line is a bit thicker so they are clearly visible and also we can avoid some nasty 1-pixel-diagonal problems. Finding the neighbors is the hard part. Generally, if two areas have some pixels which lie near enough beside each other, they can be considered neighbors. Now it doesn't make…from kleemans.ch
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