Medium technique
Hidden Singles: Find Them with Notes
In Bubble Sudoku this is a Hidden Single: With Notes.
When a color appears in only one cell’s notes in a block, it goes in that cell, even if the cell shows other colors too.
1
Read the notes across the block
BEFORE
Each open cell shows the colors that can still go in it. Most colors appear in two or three cells. Look for a color that appears only once.
2
Find the color with one place left
Red appears in only one cell: the middle of the bottom row. The Reds outside the block rule out every other open cell. That is the only place Red can go.
3
Place it
AFTER
That cell also shows Orange, Yellow, and Light Green, but they do not matter. Red has nowhere else to go, so place it. The other three dots come off.
Cells being readColor tints match the color being followed
Key Insight
Read colors, not cells. Pick a color and see how many cells in the block show it. If only one does, that color goes there, no matter how many other dots the cell has.
Related Techniques
Hidden Single: Last RemainingThe same idea without notes. Trace where a color is blocked across the board, and find the one cell left in a block where it can go.Obvious Single: With NotesAsks the opposite question: not where one color can go, but what can go in one cell. It looks for a cell with a single note left.If you’re stuck on a puzzle, see what to try next, in order.