Easy technique
Obvious Singles: Spot Naked Singles with Notes
Most sudoku guides call this a naked single. In Bubble Sudoku it is an Obvious Single: With Notes.
When a cell has only one color left in its notes, the answer is already written there. Find that single dot and place it.
1
Read the notes in one block
BEFORE
The dots in each open cell are the colors that can still go there. Four of these cells show three or four dots. Look for the cell that shows only one.
2
Find the cell with one note left
The cell at the top of the middle column has a single dot. Dark Purple is the only color that still fits there, because every other color already sits in its row, its column, or this block.
3
Place it
AFTER
A cell with one note left is already solved, so place Dark Purple. The note grows into the bubble, and the row, column, and block light up in Dark Purple, just like in a real game.
Cells being readColor tints match the color being followed
Key Insight
This is the first technique you read from your notes instead of from the bubbles. It is also the fastest check on the board. Each time you place a bubble, glance at the notes around it. Removing one color can leave a nearby cell with a single dot, and that dot is your next answer.
If you’re stuck on a puzzle, see what to try next, in order.