MergeSort_firstTry created by tyleralves - https://repl.it/@tyleralves/MergeSortfirstTry

MergeSort_firstTry.rb

testUnsorted = [7,0,2,1,5,9,12,3,19]

def mergeSort(unsorted)
  
  # Split array into two halves
  # Int division (ie: 9/2 = 4)
  if unsorted.length <= 1
    return unsorted
  end
    
  centerIndex = unsorted.length / 2
  firstHalf = unsorted[0..centerIndex-1]
  secondHalf = unsorted[centerIndex..-1]


  sortedFirst = mergeSort(firstHalf)
  sortedSecond = mergeSort(secondHalf)
  merge(sortedFirst, sortedSecond)
end



def merge(arr1, arr2)
  # Add values from arr1 (i) to merged until the current value is greater than the current value in arr2 (j)
  # When that occurs, do the same for arr2
  
  merged = []
  i = j = 0
  while i < arr1.length && j < arr2.length
    if arr1[i] < arr2[j]
      merged.push(arr1[i])
      i += 1
    else
      merged.push(arr2[j])
      j += 1
    end
  end
  
  # If reach the end of either array, append the remaining values of the other array to merged
  if i >= arr1.length
    merged.concat(arr2[j..-1])
  else
    merged.concat(arr1[i..-1])
  end
  
  return merged
end

mergeSort(testUnsorted)