Sudoku is a logic puzzle which is harder than an easy one and requires certain tactics to solve it.

Sudoku is a logic-based, combinatorial number-placement puzzle

Sudoku is one of the most popular games to develop your intelligence. Supposedly, it was invented in 1970 by Dell's puzzler in New York, who published it in his journal “Mathematical Puzzles and Logical Problems”. The further development to web Sudoku was held in Japan, where the name of the game was invented. In 2004, Sudoku was first published in the “Times” as an online game.