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 dot left in its notes, that color is the answer. Place it.
1
Read the notes in one block
BEFORE
Each dot is a color that can still go in that cell. 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 one dot: Dark Purple. Every other color is already in its row, column, or block.
3
Place it
AFTER
A cell with one dot left is solved. Place Dark Purple.
Cells being readColor tints match the color being followed
Key Insight
This is the fastest check on the board. Each time you place a bubble, look at the notes around it. Removing one color can leave a nearby cell with a single dot. That dot is your next answer.
Related Techniques
Obvious Single: Last PossibleThe same idea without notes. Count the colors in a cell’s row, column, and block, and when you see eight, the ninth is the answer.Hidden Single: With NotesAsks the opposite question: not what can go in one cell, but where one color can go. It finds answers in cells that still show several notes.If you’re stuck on a puzzle, see what to try next, in order.