Template Deletion Sudoku: Solving a Grid One Digit at a Time

What template deletion sudoku means

Template deletion sudoku flips the usual cell-by-cell approach on its head. Instead of asking what belongs in one square, you focus on a single shape or digit at a time and ask where all nine copies of it could possibly live across the whole board. A template is one complete, legal arrangement of that one digit - nine positions, exactly one in every row, one in every column, and one in every 3x3 box, with none of them clashing. For any given digit there is only a finite list of these templates, and every clue already on the grid rules a great many of them out. Template deletion sudoku is the disciplined act of writing down that list of possible arrangements and then crossing off the ones the current grid forbids. What remains is the complete set of ways that digit can still fall, and the overlap between those survivors is pure, reliable information.

Building and pruning the list

Start with a digit that already has several placements, because each fixed clue slashes the number of legal templates dramatically. Every existing copy of the digit pins one position and eliminates its row, column, and box for the rest, so a nearly complete digit might allow only a handful of templates while a sparse one allows dozens. That is why you rarely begin with a digit that has just one or two clues on the board. Once you have your working list, template deletion sudoku prunes it by testing each pattern against everything the grid already knows. The bookkeeping rewards patience far more than speed, so take the digits in order of how constrained they already are, and let the most complete ones do the early work.

Deleting the impossible templates

• Any template that places the digit where another solved shape already sits is dead immediately.
• Any template that collides with a locked candidate elsewhere on the grid can be removed.
• Templates that contradict an already-fixed pattern of a different digit fall away too.
• Whatever survives is the full, exact set of still-possible arrangements for that one digit.

Reading the survivors, one shape at a time

The real power of template deletion sudoku appears once only a few templates remain. If every surviving template places the digit in the same cell, that cell is solved outright. If no surviving template ever uses a particular cell, the digit can be erased from that cell's candidates. Overlap the survivors and the common ground becomes hard fact you could not have seen by scanning alone. The method is a natural fit for Shapedoku, where the nine digits are nine glowing shapes, so thinking one shape at a time feels intuitive rather than abstract - pick the heart or the lotus, picture every legal way it could scatter, and let the locked clues delete the impossible layouts. The pencil Notes keep your surviving positions visible, and a Hard or Extreme grid gives the technique enough friction to matter. Template deletion sudoku strains when a digit is wide open and the list balloons, so use it selectively: one well-chosen shape can unlock a grid that looked completely frozen, and it pairs beautifully with pointing pairs and box-line reductions that shorten the list before you even begin.