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December 21, 2020 20:40
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Trying to implement the suffix-tree algorithm for finding abbreviations
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# This uses the suffix-tree library (https://pypi.org/project/suffix-tree/). | |
# pip3 install suffix-tree | |
import sys | |
from suffix_tree import Tree | |
from suffix_tree.node import Internal, Leaf | |
from suffix_tree.util import UniqueEndChar | |
if len(sys.argv) <= 1: | |
print('usage: work.py game.txt') | |
sys.exit(-1) | |
# Read the list of strings. | |
fl = open(sys.argv[1]) | |
stringlist = fl.read().split('\n') | |
fl.close() | |
# Remove blank lines. | |
stringlist = [ val for val in stringlist if val ] | |
def pathstr(nod): | |
path = nod.path | |
ls = path.S[path.start:path.end] | |
return ''.join([ str(val) for val in ls if type(val) is not UniqueEndChar ]) | |
def find_best_abbrev(stringlist): | |
ils = [ ('s%d' % (ix,), val) for ix, val in enumerate(stringlist) ] | |
tree = Tree(dict(ils)) | |
best = [None, None, None] # savings, count, node | |
traverse(tree.root, (), tree, best) | |
abbrev = pathstr(best[2]) | |
#print('best: %d, %d: %r' % (best[0], best[1], abbrev,)) | |
if best[0] <= 0: | |
# Savings is zero or negative -- give up. | |
return '', 0, 0 | |
return abbrev, best[0], best[1] | |
def traverse(nod, prefix, tree, best): | |
abbrev = pathstr(nod) | |
count = len(tree.find_all(abbrev)) | |
cost = len(abbrev) | |
savings = count * (cost-2) - cost | |
if best[0] is None or savings > best[0]: | |
best[0] = savings | |
best[1] = count | |
best[2] = nod | |
#prefstr = ''.join([ str(val) for val in prefix ]) | |
#print('abbrev=%r, prefstr=%r, count=%d, save=%d: %s(%s)' % (prefstr, abbrev, count, savings, type(nod).__name__, nod)) | |
if type(nod) is Internal: | |
for ch, nod in nod.children.items(): | |
traverse(nod, prefix+(ch,), tree, best) | |
abbrevs = [] | |
origlen = sum([ len(val) for val in stringlist ]) | |
totalcount = 0 | |
while len(abbrevs) < 96: | |
abbrev, savings, count = find_best_abbrev(stringlist) | |
if not abbrev: | |
break | |
print('%r (count %d, savings %d)' % (abbrev, count, savings)) | |
abbrevs.append(abbrev) | |
totalcount += count | |
# Create a new string list by breaking existing strings on the new abbreviation. | |
ls = [] | |
for val in stringlist: | |
subls = val.split(abbrev) | |
ls.extend(subls) | |
stringlist = [ val for val in ls if val ] | |
finallen = sum([ len(val) for val in stringlist ]) | |
print('Reduced from %d char to %d using %d abbrevs; saved %d' % (origlen, finallen, totalcount, origlen-(finallen+2*totalcount))) | |
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