WiseWit Response 10535

Masyu (aka "White Pearls and Black Pearls") is played on a rectangular grid of cells (which is left off in this example but can be inferred) some of which contain either white or black circles. The goal is to draw a single continuous non-intersecting loop that properly passes through all circles. The loop must "enter" each cell it passes through from the center of one of its four sides and "exit" from a different side; all turns are therefore 90 degrees. The two varieties of circle have differing requirements for how the loop must pass through them: White circles must be traveled straight through, but the loop must turn in the previous and/or next cell in its path. Black circles must be turned upon, but the loop must travel straight through the next and previous cells in its path.