Sudoku

When I was asked what "sudoku" was, I had no idea what it was. Today I found out what it is! It’s a puzzle game that was born in Japan. (It writes 数独 in kanji, and it reads "suudoku". ) I’m a bit ashamed of not having known it.
Apparently, Sudoku has gotten so popular in England that British Airways had to ban the crews to do it when the airplane is landing or taking off.
I had seen a lot of people doing Sudoku in trains before, but had never tried. The rules are simple: place numbers 1~9 to each blank cell.(Each row. column, and each 3×3 blocks contains all the numbers from 1~9.)
































