40 lines
837 B
Ruby
40 lines
837 B
Ruby
|
# Top-down Mergesort algorithm based on not optimal ruby collection methods
|
||
|
|
# just to show divide-and-conquer paradigm, uses NlgN compares to sort an array,
|
||
|
|
# see test/merge_sort_test.rb
|
||
|
|
class Merge
|
||
|
|
def initialize(array)
|
||
|
|
@array = array
|
||
|
|
end
|
||
|
|
|
||
|
|
def sort(array = @array)
|
||
|
|
return array if array.length < 2
|
||
|
|
left, right = halves(array)
|
||
|
|
merge(sort(left), sort(right))
|
||
|
|
end
|
||
|
|
|
||
|
|
private
|
||
|
|
|
||
|
|
def halves(array)
|
||
|
|
middle = array.length / 2
|
||
|
|
[array[0..(middle - 1)], array[middle..-1]]
|
||
|
|
end
|
||
|
|
|
||
|
|
def merge(first, second)
|
||
|
|
result = []
|
||
|
|
|
||
|
|
while first.any? || second.any?
|
||
|
|
if first.empty?
|
||
|
|
result << second.shift
|
||
|
|
elsif second.empty?
|
||
|
|
result << first.shift
|
||
|
|
elsif first[0] > second[0]
|
||
|
|
result << second.shift
|
||
|
|
else
|
||
|
|
result << first.shift
|
||
|
|
end
|
||
|
|
end
|
||
|
|
|
||
|
|
result
|
||
|
|
end
|
||
|
|
end
|