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Level 1 sudoku games on this website only need two basic techniques to solve completely. At every step, one square can be solved.
- The only number (naked single)
For a square, if eight of nine numbers cannot be placed there, then the only remaining number has to be there.
- The only square (hidden single)
For a link (that is a row, a column, or a block), if a number cannot be placed in eight of the nine squares, then the number has to be in the only remaining square.
Level 2 sudoku games need more techniques as described below.
- Two (three) numbers only appear in the same two (three) squares in a link. Then all other numbers can be removed from these two (three) squares.
- Two (three, four) squares in a link have exactly the same two (three, four) possible numbers. Then these two (three, four) numbers can be removed fom other squares in the link.
- One number only appear in two or three squares in a link. These two or three squares also belong to another link. Then this number can be removed from all other squares in the second link.
Level 3 sudoku puzzles on this website can be solved using advanced techniques, such as X-wing, XY-wing, XYZ-wing, swordfish, and jellyfish. No divide-and-conquer is needed.