Rules of sudoku puzzles

The puzzle's classic is a 9x9 grid, made up of 3x3 blocks. On the initial layout some cells already contain numbers, known as "givens". The goal is to fill in the empty cells with numbers (or symbols) in each, so that each column, row, and region contains the numbers 1-9 (or different symbols) only once. So, all numbers or symbols are single.

Nowadays, you can come across various grids - 4x4, 5x5, 6x6, 7x7, 8x8, 12x12, 16x16, 25x25. In addition to that, some unique variations emerged, such as:

• A three-dimensional Sudoku puzzle invented by Dion Church and published in the Daily Telegraph in May 2005.
  
• The 2005 U.S. Puzzle Championship includes a variant called Digital Number Place: rather than givens, most cells contain a partial given - a segment of a number, with the numbers drawn as if part of a seven-segment display.
• Wei-Hwa Huang created a meta-Sudoku, where the object is to finish drawing the 5x5 grid's pentomino-region borders so as to leave a uniquely solvable puzzle with no identically-shaped regions.