Little Killer Sudoku: Rules and Solving Strategy

Read each diagonal clue precisely

Little Killer Sudoku keeps the classic requirement that every row, column, and 3x3 box contains 1 through 9 exactly once. Outside the grid, a number and arrow point toward a diagonal line of cells. The digits on that diagonal must add to the clue total. Unlike Killer Sudoku cages, the cells are not enclosed, and digits may repeat along the diagonal when they do not share a row, column, or box. Count the exact cells touched by the arrow before doing any arithmetic. A clue beginning at a corner may cross nine cells, while a clue entering near the middle may cover only two or three. Diagonals can overlap, giving one cell membership in more than one sum. Shapedoku itself replaces digits with shapes and has no arithmetic values, so these sums are not part of its classic boards. Its disciplined unit scanning is still useful, because every sum candidate must also survive the normal Sudoku restrictions.

Use minimum and maximum totals to narrow cells

The number of cells on a diagonal gives immediate bounds. A three-cell line has a minimum possible total of 6 if its cells must be distinct because they share a unit, using 1, 2, and 3. If the cells do not all see one another, repeats might lower the minimum, so inspect the geometry rather than applying a memorized cage rule. The maximum follows the same principle. A short clue near the edge is often especially strong because few combinations can reach an extreme total. For a two-cell diagonal totaling 4, possible ordered pairs include 1 and 3 or 3 and 1, while 2 and 2 is allowed only if the cells do not share a row, column, or box. Write legal combinations first, then assign them to cells. A clue total does not tell you the order of digits. Crossing candidates, box restrictions, and other diagonal clues must decide which cell receives which value.

Use overlapping clues and partial sums

Overlapping diagonals are where Little Killer becomes especially elegant. If two clues share one or more cells, compare their totals and subtract the portions you already know. Suppose one diagonal totals 20 and another overlapping diagonal totals 14, with both sharing two confirmed cells totaling 9. The remaining cells must contribute 11 to the first clue and 5 to the second. This can narrow candidates even before any exact digit is placed. Also look for diagonals that cover most of a row or box. Since a complete row totals 45, knowing the sum of seven cells immediately gives the total of the remaining two, although their order still depends on Sudoku logic. Keep a small running total near each arrow and update it after every placement. Do not treat a valid sum combination as proof by itself. The same combination may fail because of a repeated digit in a box or an unavailable candidate in a crossing column. Arithmetic and placement must agree at every step.

1. Trace the full diagonal indicated by each outside arrow.
2. Count its cells and calculate realistic minimum and maximum totals.
3. List legal digit combinations without assuming an order.
4. Use rows, columns, and boxes to remove impossible assignments.
5. Subtract confirmed digits from the clue to find the remaining total.
6. Compare overlapping diagonals and use differences to isolate shared cells.