How hint sparks work in a falling number puzzle
Learn how hint sparks and undos work in a falling number puzzle, when each one helps a stuck cell, and how to save sparks for harder boards.
On this 4x4 board, three columns are full, the fourth is nearly full, and two empty cells remain near the top. Each of the two cells could take the same number, and the solver has a finger over the tray without tapping. Every row, column and box has to contain each number exactly once, so the numbers already placed should decide the choice. At this point it is not settled, or at least the solver cannot see how.
Three things can happen next. The solver can stop and look at the rows again, checking each one for a number that cannot go in the lower cell. The solver can keep thinking for another minute, while the level timer keeps running. The solver can also spend a spark.
Sparks come only from playing NumFall and cannot be bought, so each spark in hand was earned in a finished level. Spending one is not the same as taking a free hint. Solvers in this spot often wonder whether the board is bad enough to justify a spark, or whether a closer look at the column would reveal the answer.
What each spark pays for
Sparks pay for four things. A hint points toward a cell that can be solved by logic, so the solver sees where to look next, though the reasoning still has to be done by the solver. An undo returns the last drop, which lets a solver take back a number and test another drop order. An extra heart gives the solver one more mistake allowed before the level ends. A skip moves the solver past a level without finishing it.
The hint and the undo are the two that solvers tend to compare, since both help with the stuck board described above. A hint is most useful when the solver cannot find any cell to start from. Numbers fall to the lowest empty cell and cannot be moved after they land, so an undo helps most when a number has dropped and the solver suspects the order was wrong.
Every level can be solved by logic alone, with no guessing. A solver who has no sparks left is therefore never blocked, and a level that seems stuck always has a cell that can be worked out from the numbers already placed. Sparks are optional help that saves time or effort, and no level needs one.
Spending a spark on a stuck cell
When a solver on a 6x6 board is stuck, scanning the row, column and box around the empty cell is often the first step. In a 6x6 grid each box holds six cells, so the scan is short. Next, the solver makes a list of the numbers already in those three groups and the numbers still missing. If only one number is missing from all three, the cell is solved without any help.
Usually a stuck cell has two candidates left, such as a 2 and a 5. The solver checks the drop order first, before spending anything. In a column, a number falls to the lowest empty cell, so dropping the 5 first could put it in the lower cell and leave the 2 for the upper one. The row and box rules often allow only one order, and then the cell is no longer stuck.
Sometimes an undo does more than a hint, when an earlier drop locked a cell too early. Say a 4 landed in the third cell of a column, and the cell above it can now take only a number already present in its row. A hint would send the solver to another cell, but the earlier drop is the real cause of the problem. The solver can undo the drop, which returns the 4 to the tray, and then try a different order.
Saving sparks for a Master 9x9 level
Master 9x9 levels have eighty-one cells and nine boxes, so a single scan of the board takes much longer than on a 4x4 or 6x6. Solvers often lose patience before they have actually used up their options. After several minutes of checking rows and columns, a solver may decide a hint is the only option, even though one more careful pass would have found the cell.
Before a level starts, a solver can count the sparks on hand and decide ahead of time how many to spend. With seven sparks, a solver might set aside two for hints and save the rest for undos on later levels. After the limit, the solver goes back to scanning, since logic alone can still solve the level.
Returning to that cell later, with no timer running, lets the solver see whether a row or box check would have worked without help. The next step is to open the sparks count, write down the number, and pick the limit before the first drop.
FAQ
What does a hint spark do in a falling number puzzle?
A hint points toward a cell that can be solved by logic, so the solver knows where to look next. The solver still has to work out the number from the rows, columns and boxes.
When should I use an undo instead of a hint?
The undo is the better choice when a number has dropped and the order looks wrong. Numbers fall to the lowest empty cell and cannot be moved after they land, so an early drop can lock a cell too soon.
Can a falling number puzzle be solved without spending sparks?
Yes, every level can be solved by logic alone without guessing. A stuck cell always has a value that can be worked out from the numbers already on board.
How many hints should I allow myself on a 9x9 board?
One simple plan is to count your sparks before the level starts and set a limit in advance. A player with seven sparks might allow two hints and keep the rest for later levels.
Where can I see a cell again after I used a spark on it?
The Daily Drop gives every player the same board, so you can return to it later. Looking at the spent cell without a timer shows if a row or box check would have worked on its own.
Sources
NumFall is made by the publisher of this site. Any health or brain-training points here are general information, not medical advice.