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Medium technique

Hidden Singles: Find Them with Notes

In Bubble Sudoku this is a Hidden Single: With Notes.

Sometimes a cell still shows several colors, but one of those colors has nowhere else in the block to go. That color must be the answer, no matter what else the cell shows.
1

Read the notes across the block

BEFORE

These five open cells show every color that can still go in them. Most colors appear two or three times across the block. Look for a color that appears only once.

2

Find the color with one place left

Red appears in just one cell’s notes, the middle of the bottom row. The darker Reds outside the block are the ones doing the blocking. Their rows and columns cover every other open cell in this block, but never touch the cell with the red dot. That is the only place Red can go.

3

Place it

AFTER

That cell still shows Orange, Yellow, and Light Green as well, and none of them matter. Red has nowhere else to go in this block, so Red must go there. Place it, and the other three notes come off as the bubble lands.

Cells being readColor tints match the color being followed

Key Insight

With Obvious Single you read one cell and ask what can go in it. With Hidden Single you read a whole block and ask where a color can go. The second finds answers the first misses, because a cell with four notes still looks undecided until you notice that one of its colors has nowhere else to go.

More medium techniques

If you’re stuck on a puzzle, see what to try next, in order.

Bubble Sudoku’s hints walk you through Hidden Single: With Notes on a real board, one step at a time.

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