Updates:
Labels: Difficulty-Easy
Comment #1 on issue 3702 by [email protected]: squeeze out a bit more
speed from TextDiffBuilder
http://code.google.com/p/pharo/issues/detail?id=3702
to create a cs
lcsFor: xFilteredLines and: yFilteredLines
"I find one of the longest common subsequences of my the arguments. I
assume that none of my arguments are empty. I return nil or an Array which
represents a list. The first two elements are the matching line numbers,
the last is the next node in the list or nil if there are no more elements.
The list containts the longest common subsequence. I'm a modified version
of the greedy lcs algorithm from the 6th page of 'An O(ND) Difference
Algorithm and Its Variations (1986)' by Eugene W. Myers"
| n m v lcss max |
n := xFilteredLines size.
m := yFilteredLines size.
max := m + n.
v := Array new: 2 * max + 1.
v at: max + 2 put: 0.
lcss := Array new: 2 * max + 1.
0 to: max do: [ :d |
d negated to: d by: 2 do: [ :k |
| index lcs x y |
index := max + k.
(k + d = 0 or: [ k ~= d and: [ (v at: index) < (v at:
index + 2) ] ])
ifTrue: [ x := v at: (index := index + 2) ]
ifFalse: [ x := (v at: index) + 1 ].
y := x - k.
lcs := lcss at: index.
[ x < n and: [ y < m and: [ (xFilteredLines at: x + 1) = (yFilteredLines
at: y + 1) ] ] ]
whileTrue: [
lcs := { x := x + 1. y := y + 1. lcs }
].
(x >= n and: [ y >= m ]) ifTrue: [ ^lcs ].
v at: max + k + 1 put: x.
lcss at: max + k + 1 put: lcs ] ].
self error
and
findMatches
"I find the matching pairs of xLines and yLines. First I filter out all
lines that can't have a pair, then I find the longest common subsequence of
the remaining elements. Finally I mark the matching pairs."
| temp lcs xFilteredLines yFilteredLines xNumbers yNumbers |
"Filter out all lines that can't have a pair."
temp := yLines asSet.
xFilteredLines := xLines select: [ :each |
temp includes: each ].
xFilteredLines size = 0 ifTrue: [ ^self ].
temp := xLines asSet.
yFilteredLines := yLines select: [ :each |
temp includes: each ].
yFilteredLines size = 0 ifTrue: [ ^self ].
"Map all lines to SmallIntegers, because they can be compared faster."
temp := Dictionary new.
xNumbers := xFilteredLines collect: [ :each |
temp at: each ifAbsentPut: [ temp size ] ].
yNumbers := yFilteredLines collect: [ :each |
temp at: each ifAbsentPut: [ temp size ] ].
temp := nil.
"Find the longest common subsequence."
lcs := self lcsFor: xNumbers and: yNumbers.
"Mark the matching pairs."
[ lcs == nil ] whileFalse: [
(xFilteredLines at: (lcs at: 1)) matches: (yFilteredLines at: (lcs at:
2)).
lcs := lcs at: 3 ]
