### Theory:

The puzzle 'SUDOKU' is a logic-based number placement game.

 History of 'SUDOKU'In $$18$$th Century, Swiss Mathematician's game called 'Latin Squares'. Those number puzzles were published in France in $$1985$$.  The modern game of Sudoku invented by Howard Garns, a freelance puzzle inventor from Connersville, Indiana, USA in $$1979$$ and it was published in Dell Pencil Puzzles and Word Games magazine. The puzzle was named as “Number Place”, since it involved placing individual numbers into empty spots on a $$9 \times 9$$ grid. The name 'Sudoku' is from Japan and consists of the Japanese characters Su (meaning 'number') and Doku (meaning 'single') but the was not invented in Japan. Sudoku originated in Switzerland and then traveled to Japan by way of America.
$$3\times3$$ Sudoku Rule: The idea of SUDOKU is to fill in the numbers $$1-3$$ exactly once in every row and column.
Rules to solve $$3 \times 3$$ Sudoku:
• There are $$3$$ rows and $$3$$ columns.
• Each row should be placed with the digits $$1$$, $$2$$ and $$3$$ exactly once.
• Each column contains each digit of $$1–3$$ exactly once.