add mergesort

BogoSort.rb

@@ -13,6 +13,6 @@ class Array
 	end
 end
 
-puts "Enter a list of numbers seprated by space"
+puts "Enter a list of numbers separated by spaces"
 str = gets.chomp.split('')
 puts str.bogosort.join('')

BubbleSort.rb

@@ -15,7 +15,7 @@ def bubble_sort(array)
 
   array
 end
-puts "Enter a list of numbers seprated by space"
+puts "Enter a list of numbers separated by spaces"
 
 list = gets 
 bubble_sort(list)

InsertionSort.rb

@@ -10,7 +10,7 @@ def insertion_sort(array)
   end
   array
 end
-puts "Enter a list of numbers seprated by space"
+puts "Enter a list of numbers separated by spaces"
 
 list = gets 
 insertion_sort(list)

MergeSort.rb

@@ -0,0 +1,25 @@
+def mergesort(arr) 
+  return arr if arr.length <= 1 
+  m = arr.length / 2 
+  l = mergesort(arr[0...m])
+  r = mergesort(arr[m...arr.length])
+  merge(l, r)
+end 
+
+def merge(l, r) 
+  aux = [] 
+
+  until l.empty? || r.empty? 
+    if l.first < r.first 
+      aux << l.shift 
+    else 
+      aux << r.shift 
+    end 
+  end 
+
+  aux.concat(l).concat(r)
+end 
+
+puts "Enter a list of numbers separated by spaces"
+arr = gets.chomp.split.map(&:to_i)
+puts "Sorted: #{mergesort(arr)}"

README.md

@@ -19,7 +19,15 @@ __Properties__
 
 ###### View the algorithm in [action][bubble-toptal]
 
+### Merge Sort 
+![alt text][mergesort-image]
 
+From [Wikipedia][mergesort-wiki]:   
+Conceptually, a merge sort works as follows:
+
+1. Divide the unsorted list into n sublists, each containing 1 element (a list of 1 element is considered sorted).  
+
+2. Repeatedly merge sublists to produce new sorted sublists until there is only 1 sublist remaining. This will be the sorted list.
 
 ### Insertion Sort
 ![alt text][insertion-image]
@@ -59,3 +67,6 @@ __Properties__
 [insertion-toptal]: https://www.toptal.com/developers/sorting-algorithms/insertion-sort
 [insertion-wiki]: https://en.wikipedia.org/wiki/Insertion_sort
 [insertion-image]: https://upload.wikimedia.org/wikipedia/commons/7/7e/Insertionsort-edited.png "Insertion Sort"
+
+[mergesort-wiki]: https://en.wikipedia.org/wiki/Merge_sort
+[mergesort-image]: https://upload.wikimedia.org/wikipedia/commons/c/c5/Merge_sort_animation2.gif "Merge Sort"