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#!/usr/bin/perl
    
...
print("Solution\n");
print("========\n");
print_grid($match_grid);

Original
========
...
894567321
738921564
965274183

(?:
   (?(?{ !valid(0, 0, '1') })x)(?{ local $grid_h = $grid_h; substr($gr
+id_h, 0, 1, '1'); local $grid_v = $grid_v; substr($grid_v, 0, 1, '1')
+; }) |
...
   (?(?{ !valid(8, 8, '9') })x)(?{ local $grid_h = $grid_h; substr($gr
+id_h, 80, 1, '9'); local $grid_v = $grid_v; substr($grid_v, 80, 1, '9
+'); })
)
(?{ $match_grid = $grid_h })