A quick mini Sudoku. Fill the 4×4 grid so every row, column and 2×2 box contains the numbers 1 through 4, each exactly once.
Rules
Click an empty cell, then click a number below (or type it) to fill it in.
Every row, every column, and every 2×2 box must contain each of 1–4 exactly once — a number already used correctly in that row, column or box is shown in red if you repeat it.
Arrow keys move the selected cell; Backspace, Delete or 0 clears it.
Fill in every cell correctly to solve the puzzle — pick a difficulty and press "New puzzle" any time for a fresh one.
Tips
Start with the row, column or box that already has the most numbers filled in — it narrows down the fewest possibilities fastest.