103 lines
3.5 KiB
Sed
103 lines
3.5 KiB
Sed
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# Towers of Hanoi in sed.
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#
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# @(#)hanoi.sed 8.1 (Berkeley) 6/6/93
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#
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#
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# Ex:
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# Run "sed -f hanoi.sed", and enter:
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#
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# :abcd: : :<CR><CR>
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#
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# note -- TWO carriage returns, a peculiarity of sed), this will output the
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# sequence of states involved in moving 4 rings, the largest called "a" and
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# the smallest called "d", from the first to the second of three towers, so
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# that the rings on any tower at any time are in descending order of size.
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# You can start with a different arrangement and a different number of rings,
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# say :ce:b:ax: and it will give the shortest procedure for moving them all
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# to the middle tower. The rules are: the names of the rings must all be
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# lower-case letters, they must be input within 3 fields (representing the
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# towers) and delimited by 4 colons, such that the letters within each field
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# are in alphabetical order (i.e. rings are in descending order of size).
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#
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# For the benefit of anyone who wants to figure out the script, an "internal"
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# line of the form
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# b:0abx:1a2b3 :2 :3x2
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# has the following meaning: the material after the three markers :1, :2,
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# and :3 represents the three towers; in this case the current set-up is
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# ":ab : :x :". The numbers after a, b and x in these fields indicate
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# that the next time it gets a chance, it will move a to tower 2, move b
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# to tower 3, and move x to tower 2. The string after :0 just keeps track
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# of the alphabetical order of the names of the rings. The b at the
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# beginning means that it is now dealing with ring b (either about to move
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# it, or re-evaluating where it should next be moved to).
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#
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# Although this version is "limited" to 26 rings because of the size of the
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# alphabet, one could write a script using the same idea in which the rings
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# were represented by arbitrary [strings][within][brackets], and in place of
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# the built-in line of the script giving the order of the letters of the
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# alphabet, it would accept from the user a line giving the ordering to be
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# assumed, e.g. [ucbvax][decvax][hplabs][foo][bar].
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#
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# George Bergman
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# Math, UC Berkeley 94720 USA
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# cleaning, diagnostics
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s/ *//g
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/^$/d
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/[^a-z:]/{a\
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Illegal characters: use only a-z and ":". Try again.
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d
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}
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/^:[a-z]*:[a-z]*:[a-z]*:$/!{a\
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Incorrect format: use\
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\ : string1 : string2 : string3 :<CR><CR>\
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Try again.
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d
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}
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/\([a-z]\).*\1/{a\
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Repeated letters not allowed. Try again.
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d
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}
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# initial formatting
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h
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s/[a-z]/ /g
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G
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s/^:\( *\):\( *\):\( *\):\n:\([a-z]*\):\([a-z]*\):\([a-z]*\):$/:1\4\2\3:2\5\1\3:3\6\1\2:0/
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s/[a-z]/&2/g
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s/^/abcdefghijklmnopqrstuvwxyz/
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:a
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s/^\(.\).*\1.*/&\1/
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s/.//
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/^[^:]/ba
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s/\([^0]*\)\(:0.*\)/\2\1:/
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s/^[^0]*0\(.\)/\1&/
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:b
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# outputting current state without markers
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h
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s/.*:1/:/
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s/[123]//gp
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g
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:c
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# establishing destinations
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/^\(.\).*\1:1/td
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/^\(.\).*:1[^:]*\11/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\31/
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/^\(.\).*:1[^:]*\12/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\33/
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/^\(.\).*:1[^:]*\13/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\32/
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/^\(.\).*:2[^:]*\11/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\33/
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/^\(.\).*:2[^:]*\12/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\32/
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/^\(.\).*:2[^:]*\13/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\31/
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/^\(.\).*:3[^:]*\11/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\32/
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/^\(.\).*:3[^:]*\12/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\31/
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/^\(.\).*:3[^:]*\13/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\33/
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bc
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# iterate back to find smallest out-of-place ring
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:d
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s/^\(.\)\(:0[^:]*\([^:]\)\1.*:\([123]\)[^:]*\1\)\4/\3\2\4/
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td
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# move said ring (right, resp. left)
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s/^\(.\)\(.*\)\1\([23]\)\(.*:\3[^ ]*\) /\1\2 \4\1\3/
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s/^\(.\)\(.*:\([12]\)[^ ]*\) \(.*\)\1\3/\1\2\1\3\4 /
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tb
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s/.*/Done! Try another, or end with ^D./p
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d
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