grid.ps

%!PS
% Copyright 2024 Google LLC
%
% Use of this source code is governed by an MIT-style
% license that can be found in the LICENSE file or at
% https://opensource.org/licenses/MIT.

% Some things that were attempted for day4 when I thought it was Boggle that
% might be useful on a future day.

% Returns an array of keys of the 8 positions adjacent to key, less any which
% are not in the grid.
/neighbors { % key neighbors [key1 ... key8] ; assumes /grid is the grid
  2 dict begin
    [ -1 1 1 { %for
      /i exch def -1 1 1 { %for
        /j exch def i 0 ne j 0 ne or {
          1 indexfrommark fromkey j add exch i add exch tokey
          grid 1 index known not { pop } if
        } if
      } for
    } for ] exch pop
  end
} bind def %/neighbors

% This is Boggle, which isn't what day4 wanted.
/findchain { % (XMAS)|(MAS)|(AS)|(S)|() key findchain int
  1 index empty? { pop pop 1 } { %else
    grid 1 index ascii.nul getor 2 index 0 get ne { pop pop 0 } { %else
      exch 1 1 index length 1 sub getinterval 0 3 -1 roll neighbors { %forall
        2 index exch findchain add
      } forall
      ab:b
    } ifelse
  } ifelse
} bind def %/findchain