Mini Sudoku

A 4x4 Sudoku using the digits 1 to 4. Every row, column and 2x2 box needs each digit exactly once.

How to play

1. Tap an empty cell to select it.
2. Pick a digit from 1 to 4.
3. No digit may repeat in a row, column or 2x2 box.
4. Fill the whole grid correctly to win.