This is a bicolour masyu puzzle. Instead of making one continuous loop, the goal is to make two separate loops, one blue and one red. The coloured circles must be used for the loop of the same colour, whereas black circles can be used for either colour.
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1$\begingroup$ will the two loops intersect? $\endgroup$– Omega KryptonCommented Jul 21, 2019 at 13:23
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1$\begingroup$ Covering all cells is not required in masyu. The two loops can't cross each other. $\endgroup$– JafeCommented Jul 21, 2019 at 13:25
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$\begingroup$ I'm glad you made that clear, I misread the linked rules $\endgroup$– micsthepickCommented Jul 21, 2019 at 13:32
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1 Answer
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I believe this is the unique solution:
Key steps:
Solid circle near bottom right has to be red because otherwise you can't get the red underneath it out. That rapidly resolves the ambiguous circles over on the right. Then there isn't enough space to connect the blue parts without going around the top left, which tells you which way the "arms" of the solid red circle near the top left go. The rest is straightforward.
My apologies for the inelegance of my diagram; as you may guess, I drew some things in grey before their colours were resolved.
answered Jul 21, 2019 at 14:20
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$\begingroup$ I'm afraid you are about a minute late $\endgroup$ Commented Jul 21, 2019 at 14:21
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$\begingroup$ I don't think so. Your latest solution does something illegal on the left hand edge... $\endgroup$– Gareth McCaughan ♦Commented Jul 21, 2019 at 14:22
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$\begingroup$ BTW, sorry for the sniping. I started solving before I saw there was someone else attacking it... $\endgroup$– Gareth McCaughan ♦Commented Jul 21, 2019 at 14:27
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$\begingroup$ I took a different solve path than @GarethMcCaughan. First, consider the solid circle in row 4 column 7. If it had an arm extending to the right, then a little loop chasing fences the portion of the blue loop near row 6, column 9 in the bottom right corner, forcing it to make contact with the red loop near row 9, column 7. The other key step concerns the configuration of the arms emanating from the solid red circle in row 3, column 3 - only one configuration avoids having the red loop cross the blue loop. $\endgroup$ Commented Jul 21, 2019 at 22:03