Yajilin puzzle I created for the practice of US Puzzle Championship 2009. This is one of my favorite puzzles from Nikoli.

Rules of Yajilin Puzzle

Add black squares to the grid (only in the empty spaces) so that every arrow points to the corresponding number of black squares. Black squares need not be pointed to, and cannot be adjacent horizontally or vertically. All the remaining white space must be part of a single closed loop of squares connected horizontally or vertically.

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