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I did something similar. Started with a matrix of possibilities of a-g matching real segments A-G.

Taking acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab | cdfeb fcadb cdfeb cdbaf as an example:-

ab must be a digit 1 so ab must correlate to CF. So it:-

• removes all other segments ABDEG as possibility for both a and b
  
• removes all possibilities of C or F from all others (cdefg).
  
  

Likewise the item of length 3, dab above, correlates to the segments ACF. The same function above applied to dab, ACF means that d is left only possibly matching A as C and F have been taken away from everything other than a or b.

For the item with 4 segments we do poss( "eafb", "BCDF" )

For the items with 5 segments, if there are 3 unique strings then we know:-

• The 3 letters common to all 3 will correlate to ADG
  
• The 2 letters common to only 2 of them will correlate to CF
  
• The 2 letters that only appear in once in all three will correlate to BE
  
  

For the items with 6 segments, if there are are 3 unique strings then we know:-

• The 4 letters common to all 3 will correlate to ABFG
  
• The 3 letters that only appear in 2 of them will correlate to CDE
  
  

Just applying these rules in one pass was enough to leave my map of possibilities to segments with only one match per possibility/segment.

To make it easier I pre-sorted each of the strings in my input.

Here's the above in perl: https://gist.github.com/alexgreenbank/49b3f43fcd33e96552792dd5e631499d

And here's the debug output showing the progression of the possibility maps for the first simple example given:-

DOING: abcdefg bcdef acdfg abcdf abd abcdef bcdefg abef abcdeg ab -> bcdef abcdf bcdef abcdf
len=3
   abcdefg
a: **.*...
b: ..*.***
c: **.*...
d: ..*.***
e: ..*.***
f: **.*...
g: ..*.***
len=4
   abcdefg
a: ...*...
b: ....**.
c: **.....
d: ....**.
e: ..*...*
f: **.....
g: ..*...*
len=2
   abcdefg
a: ...*...
b: ....**.
c: **.....
d: ....**.
e: ..*...*
f: **.....
g: ..*...*
DEBUG: Got 3 fives (bcdef abcdf acdfg)
len=5
   abcdefg
a: ...*...
b: ....*..
c: **.....
d: .....*.
e: ......*
f: **.....
g: ..*....
DEBUG: Got 3 sixes (bcdefg abcdeg abcdef)
len=6
   abcdefg
a: ...*...
b: ....*..
c: *......
d: .....*.
e: ......*
f: .*.....
g: ..*....