Sudoku strategies explained with graphics

Strategies


Overview Singles Naked Pairs Naked Triples Hidden Pairs Hidden Triples Naked Quads Hidden Quads Pointing Pair Pointing Triple Box Reduction X-Wing Finned X-Wing Sashimi Finned X-Wing Franken X-Wing Finned Mutant X-Wing Skyscraper Chute Remote Pairs Simple Coloring Y-Wing W-Wing Swordfish Finned Swordfish Sashimi Finned Swordfish Franken Swordfish Mutant Swordfish Finned Mutant Swordfish Sashimi Finned Mutant Swordfish Sue De Coq XYZ-Wing X-Cycle Bi-Value Universal Grave XY-Chain 3D Medusa Jellyfish Jellyfish Jellyfish Avoidable Rectangle Unique Rectangle Hidden Unique Rectangle WXYZ-Wing Firework Subset Exclusion Empty Rectangle Sue De Coq Extended SK Loop Exocet Almost Locked Sets Alternating Inference Chain Digit Forcing Chains Nishio Forcing Chains Cell Forcing Chains Unit Forcing Chains Almost Locked Sets Forcing Chain Death Blossom Pattern Overlay Bowman Bingo



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Y-Wing


If a "Bi-Value" Cell can see two other "Bi-Value" Cells that contain one candidate of the first Cell and the same other candidate, then that other candidate can not be the solution in any Cell that "sees" the two "Bi-Value" Cells where it is present.

Indeed, whatever the solution in the first Cell, the "other" candidate must be the solution in one of the two "other" Cells.


Y-Wing

In the example above the Y-Wing is formed by J2 that "sees" H1 and J9.
If candidate 5 is the solution in J2, then candidate 3 must be the solution in H1 which eliminates all candidates 3 in Row "H" (in particular in H7) and in Square "7" (in particular in J1).
If candidate 9 is the solution in J2, then candidate 3 must be the solution in J9 which eliminates all candidates 3 in Square "9" (in particular in H7) and in Row "J" (in particular in J1).
So, whatever the solution in J2, then candidates 3 in J1 and H7 are always eliminated.



You can practice this strategy by installing the SudokuCoach application on your Android™ device.

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