To celebrate Christmas this year we released a sequence of three linked puzzles on Christmas Eve, Christmas Day, and Boxing Day. If you haven’t had a chance, do give these puzzles a go! If you have tried these puzzles and would like to see the solutions, please read on.
Puzzle #1: Christmas tree sudoku
If you haven’t tried solving a so-called thermo sudoku before, getting an intuition for how the thermometers work is key. Notice that if a $1$ lies on a thermometer it must lie on the bulb, and if a $9$ lies on a thermometer it must lie at the end. This gives a good way to start the puzzle, looking at the third row from the bottom where can a $1$ go? Once you are about a third of the way into this puzzle, it more-or-less turns into a normal sudoku and is relatively straightforward to complete. Contrary to normal practice when designing a sequence of puzzles like this, this was possibly the hardest of the three puzzles. That’s why we made it so that you could still solve puzzle #2 without solving this one. Continue reading