This question was posed to me, and I was surprised that I could not find a solution (as I thought that all rook tours [open or closed] were possible). Starting from a8, could a rook visit every square on the board once, ending on f3?

I tried a few times, with a few different strategies, but I always ended up missing one square.

It’s really easy to burn pairs of rows or columns, so the problem space could be reduced…

…but at some point (4x4), I was able to convince myself that it is impossible (at least at this size and state):

…but it might be possible that shaving off column or row pairs is also discarding a solution?

    • Fleur_@aussie.zone
      41·
      6 days ago

      Diagonal move in top right corner?

      Edit: wait actually along the whole right side

      • bleistift2@sopuli.xyzEnglish
        31·
        6 days ago

        Thanks for pointing that out. That mistake was easily mendable.

        I hope I haven’t blundered somewhere else.

          • Fleur_@aussie.zone
            4·
            6 days ago

            Logical proof of why it’s not possible for your given rules of not being able to pass through squares.

            You start in white and you can only move to black. Then you have to move to white again, then black, then white, then black and so on. For a sequence with an even number of terms you have to end on black if you start in white .Since the puzzle states you have to start and end on white it’s impossible.

    • SwarmMazer@awful.systems
      12·
      6 days ago

      Rooks don’t move diagonal. I was able to do this exercise in my head on about the third try however. Start with big laps round the outside x2, then column by column to finish

      • xia@lemmy.sdf.orgOPEnglish
        2·
        6 days ago

        I may not be understanding you correctly. Can you elaborate? Feel free to use coordinates.

        • SwarmMazer@awful.systems
          3·
          6 days ago

          I am afraid that I didn’t apply any rigor here and thought I solved it. Been playing with it for a bit and see there is likely not a solution. Good fun for me.

          • SwarmMazer@awful.systems
            1·
            6 days ago

            Seems this is related to Hamiltonian path problems. The issue is there is always one square that can’t be picked up. Why could this be?

            • Fleur_@aussie.zone
              1·
              6 days ago

              So the rook has to move from a white square to a black square or a black square to a white one. This would mean the sequence would go white, black, white, black and so on for all squares. Since there is an even number of squares if the rook starts on white it must end on black but the problem states the start and end squares are both white, thus impossible to solve. Doesn’t really have anything to do with hamiltonian paths because they are loops that will fill a space. It does relate more broadly to space filling curves in general but I think a graphical approach to this problem can be a bit misleading.

              Interestingly you can pick any two white squares on the chess board and you couldn’t make a path between them in the way op is trying to.

              • SwarmMazer@awful.systems
                1·
                6 days ago

                If you take the rooks movement, and reduce each longer move to a series of single steps a1a2a3a4 for example, this becomes a Hamiltonian problem. The corners have 2 nodes, the edges three, and the core has four. Black and white indicates even or uneven distance in nodes.