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Determining which cells are to be left empty (called spaces) is as important as determining which to fill (called boxes). To solve a puzzle, one needs to determine which cells will be boxes and which will be empty. For example, a clue of "4 8 3" would mean there are sets of four, eight, and three filled squares, in that order, with at least one blank square between successive groups. The numbers are a form of discrete tomography that measures how many unbroken lines of filled-in squares there are in any given row or column. Nonograms, also known as Hanjie, Griddlers, Picross, Japanese Crosswords, Japanese Puzzles, Pic-a-Pix, "Paint by numbers" and other names, are picture logic puzzles in which cells in a grid must be colored or left blank according to numbers at the side of the grid to reveal a hidden picture.
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