Theory:

Rules to solve $$4 \times 4$$ Sudoku:
• There are $$4$$ rows and $$4$$ columns.
• Each row should be placed with the digits $$1$$, $$2$$, $$3$$ and $$4$$ exactly once.
• Each column contains each digit of $$1–4$$ exactly once.
• Each region(sub-grid) surrounded by thick lines and it can have digits $$1$$, $$2$$, $$3$$, $$4$$ once.
Example:
Let us learn how to solve sudoku with the help of following cases.

1. Understand to fill the two empty cells.

 $$4\times4$$ Sudoku:

2. Fill in correct picture with its answer.

3. $$4 \times 4$$ number sudoku.