#! /usr/bin/perl

 use strict;
 use warnings;

 use Data::Dumper;


 my $puzzle_board = create_board();
 solve ($puzzle_board);
 print_board ($puzzle_board);


 sub solve {
     my $board = shift @_;

     my $move = 1;
     my ($x, $y) = (0, 1);

# Change this number to solve more or less of the puzzle
     while ( $move < 44 ) {

         my ($newx, $newy) = calculate_move($board, $x, $y);
         print "$move: $x,$y->$newx,$newy\t";

         if ( verify_move($board, $newx, $newy) == 1 ) {
             forward($board, $x, $y, $newx, $newy);
         } elsif ( $board->[$x][$y]{trial} < 7 ) {
             $board->[$x][$y]{trial}++;
             next;
         } else {
             back($board, $x, $y, $newx, $newy);
             $x = $board->[$newx][$newy]{oldx};
             $y = $board->[$newx][$newy]{oldy};
             $move--;
             next;
         }
         ($x, $y) = ($newx, $newy);
         $move++;
     }
 }


 sub forward {

     my ($board, $x, $y, $newx, $newy) = @_;

     $board->[$newx][$newy]->{visited} = $board->[$x][$y]->{visited} +
+ 1;
     $board->[$newx][$newy]->{oldx} = $x;
     $board->[$newx][$newy]->{oldy} = $y;
 }

 sub back {

     my ($board, $x, $y, $newx, $newy) = @_;

     $board->[$newx][$newy]{trial} = 0;
     $board->[$newx][$newy]{visited} = 0;
 }

 # Assumes that it is passed valid x and y values in the board.
 sub calculate_move {

     my ($board, $x, $y) = @_;
     my ($newx, $newy) = 0;

     if ($board->[$x][$y]{trial} == 0) {
         $newx = $x + 1;
         $newy = $y + 2;
     }
     if ($board->[$x][$y]{trial} == 1) {
         $newx = $x - 1;
         $newy = $y + 2;
     }
     if ($board->[$x][$y]{trial} == 2) {
         $newx = $x + 1;
         $newy = $y - 2;
     }
     if ($board->[$x][$y]{trial} == 3) {
         $newx = $x - 1;
         $newy = $y - 2;
     }
     if ($board->[$x][$y]{trial} == 4) {
         $newx = $x + 2;
         $newy = $y + 1;
     }
     if ($board->[$x][$y]{trial} == 5) {
         $newx = $x - 2;
         $newy = $y + 1;
     }
     if ($board->[$x][$y]{trial} == 6) {
         $newx = $x + 2;
         $newy = $y - 1;
     }
     if ($board->[$x][$y]{trial} == 7) {
         $newx = $x - 2;
         $newy = $y - 1;
     }

     return ($newx, $newy);
 }

 sub verify_move {

     my ($board, $x, $y) = @_;

     if ($x > 7 || $x < 0 || $y > 7 || $y < 0) {
         return 0;
     }

     if ($board->[$x][$y]{visited} > 0) {
         return 0;
     }

     return 1;
 }

 sub create_board {
     my @board;
     my ($i, $j);


     for ( $i = 0; $i < 8; $i++ ) {
         for ( $j = 0; $j < 8; $j++ ) {
                 $board[$i][$j] = {
                 x => $i,
                 y => $j,
                 visited => 0,
                 trial => 0,
                 oldx => 0,
                 oldy => 0
             }
         }
     }


     $board[0][1] = {
         x => 0,
         y => 1,
         visited => 1,
         trial => 0
     };

     return \@board;
 }

 sub print_board {
     my $board_ref = shift @_;
     my ($i, $j);

     print Dumper  $board_ref;
     print "\nThe Chess Board\n";
     for ($i = 7; $i >= 0; $i--) {
         for ($j = 0; $j < 8; $j++) {
             printf ("%02d   ", $board_ref->[$i][$j]{visited}  );
         }
         print "\n\n";
     }
 }
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