Learn Sudoku by technique
Walk through the core techniques the engine uses, one cell at a time on a 4×4 board.
Step 1 of 5
Practice by techniqueJump straight to the technique you want to repeat with the same explanation and board.
Naked single — one cell, one answer
The highlighted row already shows three of the four digits, so the empty cell has exactly one candidate left. Place it.
row 1
Tap the highlighted cell (or press 1–4) to place the answer this step is teaching.