Merge pull request #81 from T145/master

More ruby algorithms

Author: blakeembrey

merge-sort/merge-sort.rb

@@ -0,0 +1,19 @@
+def merge_sort(a)
+  return a if a.size <= 1
+  l, r = split_array(a)
+  combine(merge_sort(l), merge_sort(r))
+end
+
+def split_array(a)
+  mid = (a.size / 2).round
+  [a.take(mid), a.drop(mid)]
+end
+
+def combine(a, b)
+  return b.empty? ? a : b if a.empty? || b.empty?
+  smallest = a.first <= b.first ? a.shift : b.shift
+  combine(a, b).unshift(smallest)
+end
+
+# a = [6, 23, 53, 1, 2, 5, 62, 61, 33, 21, 14, 6, 23].shuffle
+# p merge_sort(a)

quick-sort/quick-sort.rb

@@ -0,0 +1,33 @@
+# NOTE: Ruby has a built in sorting method, `sort!`, that actually uses a quick-sort process; this just demonstrates an implementation.
+
+def quick_sort(array) # quick sort algorithm
+  array.quick_sort!
+end
+
+def self.quick_sort!(array)
+  process(array, 0, array.size - 1)
+end
+
+private
+
+def self.process(array, left, right)
+  if left < right
+    pivot = partition(array, left, right)
+    process(array, left, pivot - 1)
+    process(array, pivot + 1, right)
+  end
+  array
+end
+
+def self.partition(array, left, right)
+  x = array[right]
+  i = left - 1
+  (left..right - 1).each do |j|
+    if array[j] <= x
+      i += 1
+      array[i], array[j] = array[j], array[i]
+    end
+  end
+  array[i + 1], array[right] = array[right], array[i + 1]
+  i + 1
+end