Some lootboxes are unsolvable

Package: Lootboxes

• 
  sph0lt0n 2026-02-15 17:52 UTC

  Some of the puzzles create by lootboxes are unsolvable -- they correspond to configurations with odd parity. The parity check

      -- Check if can be solved
      local inversions = 0
      for i = 1, #raw_pos do
          for j = i + 1, #raw_pos do
              if raw_pos[i] > raw_pos[j] then
                  inversions = inversions + 1
              end
          end
      end
  

  incorrectly includes the parity of the blank (9), which allows some configuration with odd parity to pass this test.

  I'd recommend the following code change:

      -- Check if can be solved
      local inversions = 0
      for i = 1, #raw_pos do
          for j = i + 1, #raw_pos do
              -- Only count inversions for tiles 1-8. 
              -- Skip the blank tile (9) to ensure stable parity.
              if raw_pos[i] ~= 9 and raw_pos[j] ~= 9 then
                  if raw_pos[i] > raw_pos[j] then
                      inversions = inversions + 1 
                  end
              end
          end
      end