For more info about theese strategies, take a look at this
Strategies:
- Backtracking (worst algo with checking all possible combinations)
- Naked Single
- Hidden Single
- Block-Column-Row Interactions
- Block-Block Interactions
- Naked Pair-Triplet-Quad
- Hidden Pair-Triplet-Quad
- X-Wing
- XY-Wing
More strategies are available if you want, to take a look at at the above link