merge_sort.rb

def merge(left, right)
    return left if right[0].nil?
    return right if left[0].nil?
    if left[0] < right[0]
        [left[0]] + merge(left[1..left.length], right)
    else
        [right[0]] + merge(left, right[1..right.length])
    end
end

def merge_sort(arr)
    return arr if arr.length <= 1
    half = arr.length/2
    left, right = merge_sort(arr[0..half - 1]), merge_sort(arr[half..arr.length])
    merge(left, right)
end

def time_measure
    mer_start = Time.now
    merge_sort([9,15,25,36,48,90,45,80,50,70,39,42])
    mer_end = Time.now
    puts "Elapsed time: #{mer_end.to_f - mer_start.to_f}"
    sort_start = Time.now
    [9,15,25,36,48,90,45,80,50,70,39,42].sort
    sort_end = Time.now
    puts "Elapsed time: #{sort_end.to_f - sort_start.to_f}"
end

time_measure
# p merge_sort([15,40,1,3,8, 10]) # => [1, 3, 8, 10, 15, 40]