Easy technique
Last Remaining Cell: Only One Spot Left
Also called a hidden single, or the last remaining cell. In Bubble Sudoku it is a Hidden Single: Last Remaining.
Follow one color across the board. A color cannot repeat in a row or column. Often that leaves only one cell in a block where it can go.
1
Track one color
BEFORE
Pick a color and follow it. This block has no Red yet. One Red sits above the block, in its left column. Another Red sits to the right of the block, in its top row.
2
See what the Reds block
Red cannot go in the block’s top row, because that row already has a Red. Red cannot go in the block’s left column either. That rules out five empty cells. The other three cells already have bubbles.
3
Place Red in the last cell
AFTER
Only one cell is left, so Red goes there. Place it. You did not need any notes. The two Reds on the board showed you the answer.
Cells being readColor tints match the color being followed
Key Insight
You will use this more than any other technique on Easy and Medium boards. Pick a color that appears many times. Check one block at a time. Rule out every cell that shares a row or column with that color. Often only one cell is left.
Related Techniques
Hidden Single: With NotesThe same idea read from notes. Instead of tracing where a color is blocked, look for a color that appears in only one cell’s notes.If you’re stuck on a puzzle, see what to try next, in order.