2. Start position
I use Extreme #70 as
an example to show
the basic steps in
solving a Str8ts puzzle.
Please make sure to
read my strategy slides
(link at the end) in
order to understand
the strategies used.
3. Only once per
line and row
Str8ts rules state that
a number may only
appear once in a row
and column.
Hence we can remove
all candidates marked
yellow here.
4. Range check
All numbers within a
compartment must be
in a continues range.
Gaps are not allowed.
For example, 6 is
impossible in C2,
because there’s a 3 in
C3 and thus highest
value reachable in the
C234 compartment is
5.
5. Range check
Compartment range
checks also work if
there are still two or
more candidates in a
field.
Look at BCDE4: as the
highest candidate in
C4 is 5, we cannot
reach a higher number
than 8 in the
compartment 9 can
be removed.
6. Stranded digits
Some candidates may
become detached
from others: they are
stranded.
In G3456 2 and 3 are
stranded digits, as
they are detached
from the others. No
valid range can be
formed with them.
Next, check ranges
again (e.g. in F56).
7. High/low check
Next we do a high/low
cross-compartment
check: we see that 4
and 5 have to occur in
C24, thus we can
remove them from
C679 ( C9=6h).
Same for 456 in HJ2:
we know that these
numbers must appear
in A..F2, as they are
sure candidates there.
8. Repeat
With C9=6, we remove
the 6s in row C and
column 9, then check
the compartment
ranges again: B9 can
only be 5 or 7, and as
C7 is now 89, we can
remove 123 from
A..E7.
9. And Repeat
Next, check
compartment ranges
again, then again for
those compartments
where something
changed, then
high/low checks: this
leads to G8=2h (as
G3456 has 5 as sure
candidate).
10. Single
Some compartment
range checks, removal
of stranded digits, and
high/low checks later,
we arrive at this
position.
As the compartment
FGH9 has 3 as sure
candidate and 3 only
appears in G9, we can
set G9=3s.
11. More stranded
digits
Have a look at E78: E7
cannot be 6, because
E8 would be 8, an
invalid range. Same for
E7=8 E8=6. Thus we
can remove 68 from E7.
Same for 4 in J7: J7=4
would leave H7=12,
which is impossible.
Applying rules again,
we solve J7: J7=23d
J6=24c J7=3d!
12. Solving…
So we keep applying
these strategies and
remove candidates and
check for singles:
H9=1s (single in row H)
F9=2c
F12=4567h
DEF1=3567c
DEF1=567d, i.e. D1=5d
D8=6
D7=7
20. Swordfish on 4
We can apply the
Swordfish strategy on 4:
the blue fields make up
a row-based swordfish
that removes the 4s in
A2 and A3.
Next, 5 is a stranded
digit in A123, so we get:
A3=2w4
D3=4
E3=5
22. Solution
That’s it.
When solving a Str8ts
puzzle, you just have
to apply the same
strategies over and
over again. The hard
part is spotting
everything.
For a list of common
strategies see my
strategy slides (link at
the end).
23. Glossary
Letters appended to steps indicate the last strategy used, just before filling in a field:
• No letter … number was last candidate in field
• s … single (last) candidate for that number in compartment
• c … compartment range check
• d … stranded (unreachable/impossible) digits removed
• h … high/low range check across compartments
• p/t/q … naked pair / naked triple / naked quadruple
• ph/th/qh … hidden pair / hidden triple / hidden quadruple
• x … X-wing (2 rows / 2 columns)
• w … Swordfish (3 rows / 3 columns)
• j … Jellyfish (4 rows / 4 columns)
• L … large gap field
• Sx … Setti’s rule (count the numbers rule) – ‘x’ is the analysed number
• u … unique rectangle
• y … Y-Wing or XY-chains
24. Weekly Extreme Str8ts Puzzle #70
Solution by SlowThinker
Note: there are other (maybe easier) ways to solve this puzzle.
View & download my strategy slides from:
http://slideshare.net/SlowThinker/str8ts-basic-and-advanced-strategies
or from Google Docs:
http://is.gd/slowthinker_str8ts_strategy
