# filiptepper/introduction-to-algorithms

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 # http://en.wikipedia.org/wiki/Merge_sort class MergeSort class << self def sort array return array if array.length <= 1 left, right = [], [] middle = (array.length / 2).round 0.upto(middle - 1) { |i| left.push array[i] } middle.upto(array.length - 1) { |i| right.push array[i] } left = self.sort left right = self.sort right merge left, right end private def merge left, right result = [] i, j = 0, 0 p, r = left.length, right.length # sentinel left.push 1.0/0 right.push 1.0/0 0.upto(p + r - 1) do |k| if left[i] <= right[j] result[k] = left[i] i += 1 else result[k] = right[j] j += 1 end end result end end end if \$0 == __FILE__ require "test/unit" class MergeSortTest < Test::Unit::TestCase def test_merge_sort_with_sentinel sorted_array = MergeSort.sort [6, 3, 1, 2, 4, 8, 7, 5] assert_equal [1, 2, 3, 4, 5, 6, 7, 8], sorted_array end end end
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