The following describes the two strategies which are required for solving a SIKAKU puzzle.
When specific cells need to be referred to in this discussion, they will be designated as C4-R3 which means the 4th cell in row 3.
Unique Rectangle Strategy.
Look at C7-R8. This cell is required to be part of a rectangle of area 2. There is only one way this can be drawn as shown in the right hand
graphic.
Then look at C8-R8. There is only one way this cell can be part of a rectangle of area 5.
Now look at C6-R2. After drawing the previous two rectangles, there is only one way in which this cell can be part of a rectangle of area 9.
If you search this puzzle for more unique rectangles you will find that there are no more to be found.
"Only way to Cover" Strategy.
The aim of this strategy is to find a cell which can be covered in only one way. Such a cell is C6-R4. The only way it can be covered is by means
of the rectangle of area 10 as shown in the right hand graphic.
From this point on, there are plenty of unique rectangles to be found, and the solution can be completed without recourse to the "Only way to Cover"
Strategy. Most SIKAKU puzzles can be solved using mainly Unique Rectangles, with only an occasional use of the "Only way to Cover" Strategy.
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