Ripple strategy: the three deductions

Every Ripple board can be finished with three moves and nothing else. Learn them in order and you will never need the hint button.

One: the zero rule

A clue of 0 is a source. Distance zero exists only at the source itself, so a 0 both tells you where a source is and tells you that no other source can be within one step of it.

After marking it, immediately cross off every orthogonal neighbour. Those cells are now known non-sources, and that knowledge propagates into the next deduction.

Two: diamond elimination

A clue with value v rules out every cell within v−1 steps as a source. On a grid, "within n steps" is a diamond, not a square — it grows one cell in each direction per step, so the corners of the bounding square are not eliminated.

That shape is the single most common mistake. A clue of 3 does not clear a 7×7 square; it clears a diamond with 25 cells and leaves the four corner regions of that square untouched.

Two clues close together eliminate two overlapping diamonds. The overlap is where the information lives: cells cleared by both are gone twice over, and cells cleared by one but not the other are constraining.

Three: the counting finish

Because the board has exactly K sources, the count itself is a deduction:

• When you have placed K−1 sources, every unplaced cell that could be a source is ruled out — so if exactly one candidate remains, it is the last source.
• When you have placed K, stop: nothing else can be a source, so any remaining candidate must be wrong.

The counting finish looks trivial and is not. Most boards end not with a clever geometric deduction but with "only one candidate survives, and I still need one more source".

What a stuck position actually means

Ripple boards are generated by propagation: a clue is kept only if the board remains solvable without guessing. So being stuck is always a missed clue, never a board that requires a guess.

When you stall, do not guess. Instead:

1. Re-read the smallest clue you have not fully processed. Small numbers eliminate little, which makes them easy to skip and easy to mis-apply.
2. Check the edges. A 1 in a corner has two candidate neighbours; a 1 in the middle has four.
3. Check for a clue whose diamond you have only half applied. This is the most common stall on 10×10.

Board size and what changes

The rules do not change with size, but the difficulty profile does:

Does it transfer from Sudoku?

Partly. Sudoku trains you to hold several candidate sets at once, which helps. But Ripple's deductions are geometric — you are clearing regions, not eliminating digits — so a strong sudoku solver starts at roughly the same place as anyone else.

If you want the set-based version of the same pleasure, the sudoku collection here has thirteen rule variants and six material editions. The sudoku guide covers the techniques that carry over.