Kakuro is a puzzle game that's a cross between both traditional crosswords and Sudoku. Just like Sudoku you must fit the digits 1 to 9 into a grid of squares so that no digit 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, just like in a crossword, 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 puzzle doesn't submit well to random guessing because there are a very large number of possible number combinations, so they are best solved using logic. Some of the same logic can be used as in Sudoku, but you also need a bit of maths because unlike in Sudoku there is a second restraint: Not only must the digits 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. If the clue '4' is given for a run of two squares then the two digits that make it up must be '1' and '3', since '2' and '2' cannot be the answer because this would repeat a digit. '0' is never allowed so '4' is not an option. Therefore it can be deduced that the two cells each contain either 1 or 3. And then via a process of similar deductions and reasoning somewhat akin to Sudoku the puzzle can be solved. When you are not sure for one number or more you can activate the pencil function of Kakuro just by pressing the button labeled PENCIL. What this button does is that it allows you to mark several numbers that could possibly be part of the solution.
When you are finished you have to press the PEN button to
return to normal number filling and finish the puzzle!