Sudoku Solving Techniques

TIP: Even with all these techniques, the best way to solve these puzzles is to practice, practice and practice more...

1. Naked Single
   It is often the case that a cell can only possibly take a single value, when the contents of the other cells in the same row, column and block are considered. (Read More...)
   
   
2. Hidden Single
   If a cell is the only one in a row, column or block that can take a particular value, then it must have that value. (Read More...)
   
   
3. Block and Column / Row Interactions
   Sometimes, when you examine a block, you can determine that a certain number must be in a specific row or column, even though you cannot determine exactly which cell in that row or column. (Read More...)
   
   
4. Block / Block Interactions
   If a number appears as candidates for two cells in two different blocks, but both cells are in the same column or row, it is possible to remove that number as a candidate for other cells in that column or row. (Read More...)
   
   
5. Naked Subset
   If two cells in the same row, column or block have only the same two candidates, then those candidates can be removed from other cells in that row, column or block. This technique can also be extended to cover more than two cells. (Read More...)
   
   
6. Hidden Subset
   This technique is very similar to naked subsets, but instead of affecting other cells with the same row, column or block, candidates are eliminated from the cells that hold the hidden subset.
   (Read More...)
   
   
7. X-Wing
   This is another method of reducing the candidates when two rows have the same candidate only in the same two columns. (Read More...)
   
   
8. Swordfish
   Swordfish is on the same principle as X-wings, but extended to three columns or rows.
   (Read More...)
   
   
9. XY-Wing
   This is similar to a short forcing chain with only two links for each candidate. (Read More...)
   
   
10. XYZ-Wing
    This is a variation of an XY-wing. (Read More...)
    
    
11. Colouring
    Colouring considers cells where a particular candidate occurs for only two cells in a unit.
    (Read More...)
    
    
12. Remote Pairs
    This technique is a combination of naked pairs and colouring. (Read More...)
    
    
13. XY Chains
    XY chains allow you to make eliminations by following a chain of cells that have only two candidates each. (Read More...)
    
    
14. Forcing Chains
    Forcing chains is a technique that allows you to deduce with certainty the content of a cell from considering the implications resulting from the placement of each of another cell's candidates. (Read More...)
    
    
15. Nishio
    This is limited form of trial and error. It asks what are the effects of putting a particular number into a particular cell? (Read More...)
    
    
16. Trial and Error
    There are some that would argue trial and error is not a logical technique, and is no better than guessing. When further moves seem impossible, trial and error may be the only way forward. (Read More...)