I got addicted to Sudoku last year and I am still playing this number puzzle on daily basis. Few weeks ago, I got addicted to sumdoku (or killer sudoku), which is even more challenging.

Sudoku (数独 sūdoku?), also known as Number Place or Nanpure, is a logic-based placement puzzle. The aim of the puzzle is to enter the digits 1 through 9 in each cell of a 9×9 grid made up of 3×3 subgrids (called “regions”) so that each row, column, and region contains exactly one instance of each digit. A set of clues, or “givens”, constrain the puzzle such that there is only one way to correctly fill in the remainder.
The modern puzzle Sudoku was invented in Indianapolis in 1979 by Howard Garns. Garns’ puzzles appeared in Dell Magazines, which published them under the title “Number Place”. Sudoku became popular in Japan in 1986, when puzzle publisher Nikoli discovered the game in older Dell publications. The puzzles became an international hit in 2005.

Personally, I prefer Sumdoku, it is very hard to crack at the begining, but once you get the first few clues, the rests are just piece of cake.

	PROTECT YOUR FAMILY GET QUOTE Best Deal Insurers Annual Travel Insurance Buildings and Contents Insurance

Killer sudoku (also killer su doku, sumdoku, sum doku, addoku, or samunamupure) is a puzzle that combines elements of sudoku and kakuro. Despite the name, the simpler killer sudokus can be easier to solve than regular sudokus, depending on the solver’s skill at mental arithmetic; the hardest ones, however, can take hours to crack.
A typical problem is shown on the right, using colors to define the groups of cells. More usually, puzzles are printed in black and white, with thin dotted lines used to outline the “cages”.

Next, I will introduce some cool sudoku websites, so you can kill your time in your office.

Also, you can purchase the books of Sudoku puzzle in the auction below. Good luck!