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Kakuro is a puzzle game that's a cross between both traditional crosswords and Sudoku. The idea behind Kakuro is very simple. Just like Sudoku you must fit the numbers 1 to 9 into a grid of squares so that no number is repeated within a defined area. And just like a crossword there's a grid of filled blocks and clues to solve. In Kakuro, there are across and down clues, but they give the sum of the digits in the relevant areas--which is why the puzzles are also called Cross Sums. The clues are written within the grid to the left or the top of the area they apply to. As in Sudoku, the puzzles are best solved using logic. Some of the same logic can be used as in Sudoku, but you also need a bit of math because unlike in Sudoku there is a second restraint: Not only must the numbers not repeat within a clue run but they also must add up to given totals--these totals replace the traditional word clues found in a crossword.