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# Use "An O(NP) Sequence Comparison Algorithm" as described by Sun Wu, Udi Manber and Gene Myers
# in http://www.itu.dk/stud/speciale/bepjea/xwebtex/litt/an-onp-sequence-comparison-algorithm.pdf
class ONPDiff
def initialize(a, b)
@a, @b = a, b
@m, @n = a.length, b.length
@backtrack = []
if @reverse = @m > @n
@a, @b = @b, @a
@m, @n = @n, @m
end
@offset = @m + 1
@delta = @n - @m
end
def diff
@diff ||= build_edit_script(compose)
end
def short_diff
@short_diff ||= build_short_edit_script(compose)
end
private
def compose
return @shortest_path if @shortest_path
size = @m + @n + 3
fp = Array.new(size) { |i| -1 }
@path = Array.new(size) { |i| -1 }
p = -1
begin
p += 1
k = -p
while k <= @delta - 1
fp[k + @offset] = snake(k, fp[k - 1 + @offset] + 1, fp[k + 1 + @offset])
k += 1
end
k = @delta + p
while k >= @delta + 1
fp[k + @offset] = snake(k, fp[k - 1 + @offset] + 1, fp[k + 1 + @offset])
k -= 1
end
fp[@delta + @offset] = snake(@delta, fp[@delta - 1 + @offset] + 1, fp[@delta + 1 + @offset])
end until fp[@delta + @offset] == @n
r = @path[@delta + @offset]
@shortest_path = []
while r != -1
@shortest_path << [@backtrack[r][0], @backtrack[r][1]]
r = @backtrack[r][2]
end
@shortest_path
end
def snake(k, p, pp)
r = p > pp ? @path[k - 1 + @offset] : @path[k + 1 + @offset]
y = [p, pp].max
x = y - k
while x < @m && y < @n && @a[x] == @b[y]
x += 1
y += 1
end
@path[k + @offset] = @backtrack.length
@backtrack << [x, y, r]
y
end
def build_edit_script(shortest_path)
ses = []
x, y = 1, 1
px, py = 0, 0
i = shortest_path.length - 1
while i >= 0
while px < shortest_path[i][0] || py < shortest_path[i][1]
if shortest_path[i][1] - shortest_path[i][0] > py - px
t = @reverse ? :delete : :add
ses << [@b[py], t]
y += 1
py += 1
elsif shortest_path[i][1] - shortest_path[i][0] < py - px
t = @reverse ? :add : :delete
ses << [@a[px], t]
x += 1
px += 1
else
ses << [@a[px], :common]
x += 1
y += 1
px += 1
py += 1
end
end
i -= 1
end
ses
end
def build_short_edit_script(shortest_path)
ses = []
x, y = 1, 1
px, py = 0, 0
i = shortest_path.length - 1
while i >= 0
while px < shortest_path[i][0] || py < shortest_path[i][1]
if shortest_path[i][1] - shortest_path[i][0] > py - px
t = @reverse ? :delete : :add
if ses.length > 0 && ses[-1][1] == t
ses[-1][0] << @b[py]
else
ses << [@b[py], t]
end
y += 1
py += 1
elsif shortest_path[i][1] - shortest_path[i][0] < py - px
t = @reverse ? :add : :delete
if ses.length > 0 && ses[-1][1] == t
ses[-1][0] << @a[px]
else
ses << [@a[px], t]
end
x += 1
px += 1
else
if ses.length > 0 && ses[-1][1] == :common
ses[-1][0] << @a[px]
else
ses << [@a[px], :common]
end
x += 1
y += 1
px += 1
py += 1
end
end
i -= 1
end
ses
end
end
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