The game player can request a hint by either selecting Hint from the Game Menu, or typing he letter "H" during game play. When the Sudoku applet gives the user a hint, it tells the user what digit can be placed at a specified row and column on the game board, and it places the digit entry cursor at that square. In addition, graphical symbols are placed on the board to tell the user how it figured out the hint play. The hint clue symbols follow.
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The row clue consists of a diamond with a horizontal line to the lower right. This clue indicates that the number in the diamond cannot occur again on this row.
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The column clue consists of a diamond with a verticle line to the lower right. This clue indicates that the number in the diamond cannot occur again on this column.
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The box or mini-grid clue consists of a diamond with a small square to the lower right. This clue indicates that the number in the diamond cannot occur again in this box or mini-grid.
Note that for a box clue the small box may contain a horizontal or vertical line that indicates that the digit in the diamond is not allowed in this row or column, respectively (see below).
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If no logical rule is found that can determine the next play, the Sudoku applet will find a row, column, or box where there are only two possible places where particular digit may be placed. This will be indicated by two circles on empty squares. The user may guess one of the two circled locations, and if it does not subsequently work out, go back and place the digit in the other location.
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For the box clue, if the box contains a vertical or horizontal line, this points out that the digit in addition to not being allowed again in the box or mini-grid, it is also not allowed in the column or row, respectively.
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If a digit must be in one of three positions of a sub-row or sub-column in a mini-grid, this may be refered to as forcing, and this will prevent the digit from being placed in the respective game board row or column outside of the mini-grid. Here we see an example where the number 2 must exist in a mini-grid sub-row.
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If for two positions in a row, column or mini-grid there are two squares where the same two digits must exist, as when each square may only contain a 5 or 6, the squares may be called twins. The twin digits are then precluded from the remainder of that row, column or mini-grid respectively.
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If for three positions in a row, column or mini-grid there are three squares where the same three digits must exist, as when each square may contain only one of 4, 8 or 9, the squares are called triples. The triples digits are then precluded from the remainder of that row, column or mini-grid.
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