Solving Sudoku - Tactics part 2
Continuing with the tactics for solving Sudoku from my earlier post, here is the second part of the post. Here we will discuss tactics referring to level 2 and 3. For legend and terminologies please refer the earlier post.
Level Two:
The tactics are quite elementary, in that one would observe that these are applied to almost most of the sudokus of difficulty levels greater than two. These are also very easy to calculate and present a very powerful and easy tool to solve the tactics.
Naked Pairs
If a pair of Ns are the only possibilities in two Ps of a R or C or B, then exclude those Ns from the rest of Ps in that R or C or B
Hidden Pairs
If a pair of Ns are locked in two Ps of a R or C or B, then remove other Ns from those two Ps
The below 2 tactics are also useful and one might find them used often in the sudokus of difficulty level 4 and 5. It starts to get little clumsy to note down the possibilities and find triplet combination as we start making some note at the edge of every cell, but I know of no other way.
Naked Triplets
If a triplet of Ns are the only possibilities in three Ps of a R or C or B, then exclude those Ns from the rest of Ps in that R or C or B
Hidden Triplets
If a triplet of Ns are locked in three Ps of a R or C or B, then remove other Ns from those three Ps
Level Three:
These tactics are similar to the level two tactics, except that we also need to figure out the number of cells that are involved in the set (unlike in the earlier levels) apart from the figuring out the N's and cells involved. Without these two tactics it is sometimes very hard, rather I should say impossible to solve sudokus of difficulty level 5.
Naked Set
If a set of 'k' Ns are the only possibilities in 'k' Ps of a R or C or B, then exclude those Ns from the rest of Ps in that R or C or B
Hidden Set
If a set of 'k' Ns are locked in k Ps of a R or C or B, then remove other Ns from those 'k' Ps
Level Two:
The tactics are quite elementary, in that one would observe that these are applied to almost most of the sudokus of difficulty levels greater than two. These are also very easy to calculate and present a very powerful and easy tool to solve the tactics.
Naked Pairs
If a pair of Ns are the only possibilities in two Ps of a R or C or B, then exclude those Ns from the rest of Ps in that R or C or B
Hidden Pairs
If a pair of Ns are locked in two Ps of a R or C or B, then remove other Ns from those two Ps
The below 2 tactics are also useful and one might find them used often in the sudokus of difficulty level 4 and 5. It starts to get little clumsy to note down the possibilities and find triplet combination as we start making some note at the edge of every cell, but I know of no other way.
Naked Triplets
If a triplet of Ns are the only possibilities in three Ps of a R or C or B, then exclude those Ns from the rest of Ps in that R or C or B
Hidden Triplets
If a triplet of Ns are locked in three Ps of a R or C or B, then remove other Ns from those three Ps
Level Three:
These tactics are similar to the level two tactics, except that we also need to figure out the number of cells that are involved in the set (unlike in the earlier levels) apart from the figuring out the N's and cells involved. Without these two tactics it is sometimes very hard, rather I should say impossible to solve sudokus of difficulty level 5.
Naked Set
If a set of 'k' Ns are the only possibilities in 'k' Ps of a R or C or B, then exclude those Ns from the rest of Ps in that R or C or B
Hidden Set
If a set of 'k' Ns are locked in k Ps of a R or C or B, then remove other Ns from those 'k' Ps
How to determine k in the above tactic is by observation only. I usually attempt the level 3 tactic at the end since it is time consuming to figure it out as it involves observation.
We will discuss the higher level tactics next week..
until then Happy Sudoku Solving..!
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