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