Book excerpt: Kakuro is already sweeping Japan--it's a phenomenon even more addictive than sudoku--and now it's here. An ingenious blend of numbers and logic, kakuro offers the supreme challenge for puzzlers of all ages. It's played on grids of various sizes, offering different levels of difficulty. The object is to make each row add up to the number given at the top (for down rows) or the left (for across rows). Like sudoku, it uses only the numbers from 1 to 9, each appearing no more than once in each row. Here are 200 irresistibly engaging puzzles, graded from "Easy" to "Fiendish," plus tips on how to master them. Win or lose, it always adds up to fun.