mirror of
https://github.com/freebsd/freebsd-src.git
synced 2024-11-28 19:52:44 +00:00
103 lines
3.5 KiB
Sed
103 lines
3.5 KiB
Sed
# Towers of Hanoi in sed.
|
|
#
|
|
# @(#)hanoi.sed 8.1 (Berkeley) 6/6/93
|
|
#
|
|
#
|
|
# Ex:
|
|
# Run "sed -f hanoi.sed", and enter:
|
|
#
|
|
# :abcd: : :<CR><CR>
|
|
#
|
|
# note -- TWO carriage returns, a peculiarity of sed), this will output the
|
|
# sequence of states involved in moving 4 rings, the largest called "a" and
|
|
# the smallest called "d", from the first to the second of three towers, so
|
|
# that the rings on any tower at any time are in descending order of size.
|
|
# You can start with a different arrangement and a different number of rings,
|
|
# say :ce:b:ax: and it will give the shortest procedure for moving them all
|
|
# to the middle tower. The rules are: the names of the rings must all be
|
|
# lower-case letters, they must be input within 3 fields (representing the
|
|
# towers) and delimited by 4 colons, such that the letters within each field
|
|
# are in alphabetical order (i.e. rings are in descending order of size).
|
|
#
|
|
# For the benefit of anyone who wants to figure out the script, an "internal"
|
|
# line of the form
|
|
# b:0abx:1a2b3 :2 :3x2
|
|
# has the following meaning: the material after the three markers :1, :2,
|
|
# and :3 represents the three towers; in this case the current set-up is
|
|
# ":ab : :x :". The numbers after a, b and x in these fields indicate
|
|
# that the next time it gets a chance, it will move a to tower 2, move b
|
|
# to tower 3, and move x to tower 2. The string after :0 just keeps track
|
|
# of the alphabetical order of the names of the rings. The b at the
|
|
# beginning means that it is now dealing with ring b (either about to move
|
|
# it, or re-evaluating where it should next be moved to).
|
|
#
|
|
# Although this version is "limited" to 26 rings because of the size of the
|
|
# alphabet, one could write a script using the same idea in which the rings
|
|
# were represented by arbitrary [strings][within][brackets], and in place of
|
|
# the built-in line of the script giving the order of the letters of the
|
|
# alphabet, it would accept from the user a line giving the ordering to be
|
|
# assumed, e.g. [ucbvax][decvax][hplabs][foo][bar].
|
|
#
|
|
# George Bergman
|
|
# Math, UC Berkeley 94720 USA
|
|
|
|
# cleaning, diagnostics
|
|
s/ *//g
|
|
/^$/d
|
|
/[^a-z:]/{a\
|
|
Illegal characters: use only a-z and ":". Try again.
|
|
d
|
|
}
|
|
/^:[a-z]*:[a-z]*:[a-z]*:$/!{a\
|
|
Incorrect format: use\
|
|
\ : string1 : string2 : string3 :<CR><CR>\
|
|
Try again.
|
|
d
|
|
}
|
|
/\([a-z]\).*\1/{a\
|
|
Repeated letters not allowed. Try again.
|
|
d
|
|
}
|
|
# initial formatting
|
|
h
|
|
s/[a-z]/ /g
|
|
G
|
|
s/^:\( *\):\( *\):\( *\):\n:\([a-z]*\):\([a-z]*\):\([a-z]*\):$/:1\4\2\3:2\5\1\3:3\6\1\2:0/
|
|
s/[a-z]/&2/g
|
|
s/^/abcdefghijklmnopqrstuvwxyz/
|
|
:a
|
|
s/^\(.\).*\1.*/&\1/
|
|
s/.//
|
|
/^[^:]/ba
|
|
s/\([^0]*\)\(:0.*\)/\2\1:/
|
|
s/^[^0]*0\(.\)/\1&/
|
|
:b
|
|
# outputting current state without markers
|
|
h
|
|
s/.*:1/:/
|
|
s/[123]//gp
|
|
g
|
|
:c
|
|
# establishing destinations
|
|
/^\(.\).*\1:1/td
|
|
/^\(.\).*:1[^:]*\11/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\31/
|
|
/^\(.\).*:1[^:]*\12/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\33/
|
|
/^\(.\).*:1[^:]*\13/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\32/
|
|
/^\(.\).*:2[^:]*\11/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\33/
|
|
/^\(.\).*:2[^:]*\12/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\32/
|
|
/^\(.\).*:2[^:]*\13/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\31/
|
|
/^\(.\).*:3[^:]*\11/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\32/
|
|
/^\(.\).*:3[^:]*\12/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\31/
|
|
/^\(.\).*:3[^:]*\13/s/^\(.\)\(.*\1\([a-z]\).*\)\3./\3\2\33/
|
|
bc
|
|
# iterate back to find smallest out-of-place ring
|
|
:d
|
|
s/^\(.\)\(:0[^:]*\([^:]\)\1.*:\([123]\)[^:]*\1\)\4/\3\2\4/
|
|
td
|
|
# move said ring (right, resp. left)
|
|
s/^\(.\)\(.*\)\1\([23]\)\(.*:\3[^ ]*\) /\1\2 \4\1\3/
|
|
s/^\(.\)\(.*:\([12]\)[^ ]*\) \(.*\)\1\3/\1\2\1\3\4 /
|
|
tb
|
|
s/.*/Done! Try another, or end with ^D./p
|
|
d
|