How to Check a Completed Sudoku Solution

Check rows as complete symbol sets

Begin with the first row and confirm that all nine symbols appear exactly once. In classic Sudoku, that means the digits 1 through 9. In Shapedoku, look for one triangle, hexagon, circle, crystal, heart, diamond, square, crescent moon, and lotus flower. Do not simply count nine filled cells. A row can be full while containing one duplicate and one missing symbol. Scan in a fixed symbol order so your eyes do not skip over similar positions. If you find a duplicate, note both cells but do not change either one immediately. The wrong entry may be in a crossing column or box, and replacing the first suspicious cell can create a second mistake. Finish checking all nine rows and record every conflict before making repairs.

Repeat the audit for columns and boxes

After rows, inspect columns from left to right. Then check the nine 3 by 3 boxes in reading order. A valid solution must pass all three tests. Rows alone are not enough because two symbols can be swapped within a row while preserving its complete set. Columns and boxes expose that error. Use completed units as evidence: if one cell participates in a bad row and a bad column, it deserves attention. If two suspicious cells share the same row, column, or box, compare which symbols are missing from their crossing units. On a printed puzzle, place a small tick beside each verified unit rather than marking cells. On screen, move slowly through the board and keep the same order. Human eyes are remarkably willing to approve a pattern they have already stared at for twenty minutes.

Trace errors back to the smallest conflict

When a unit contains a duplicate, identify the missing symbol and inspect the two duplicate cells against their other units. Suppose a row contains two hearts and no lotus. Check the columns and boxes of both heart cells. If one of those crossing units is also missing a lotus, that cell is a strong candidate for correction. Still verify the replacement against all three units before entering it. If several conflicts overlap, undo the most recent uncertain placements instead of trying random swaps. The free Shapedoku solver can also check a copied puzzle, but enter the original clues rather than treating your entire completed grid as fixed. Ask for step-by-step help so the solver can reveal where your logical path diverged. A verification routine should identify the fault while preserving as much of your valid work as possible.

1. Check all nine rows for one copy of every symbol.
2. Check all nine columns using the same symbol order.
3. Check all nine boxes in reading order.
4. Record duplicates and missing symbols before changing any cell.
5. Use crossing units to identify the smallest likely error.
6. Verify every correction against its row, column, and box.