Quicksort implementation added

merge_sort.rb

@@ -0,0 +1,58 @@
+"""
+Algorithm: Quicksort
+Time Complexity: O(nlogn)
+"""
+def quicksort(array, from_idx=0, to_idx=nil)
+    if to_idx == nil
+        # Sort the whole array, by default
+        to_idx = array.count - 1
+    end
+
+    if from_idx >= to_idx
+        # Base case
+        return
+    end
+
+    # Take a pivot value, at the far left
+    pivot = array[from_idx]
+
+    # Min and Max pointers
+    min = from_idx
+    max = to_idx
+
+    # Current free slot
+    free = min
+
+    while min < max
+        if free == min # Evaluate array[max]
+            if array[max] <= pivot # Smaller than pivot, must move
+                array[free] = array[max]
+                min += 1
+                free = max
+            else
+                max -= 1
+            end
+        elsif free == max # Evaluate array[min]
+            if array[min] >= pivot # Bigger than pivot, must move
+                array[free] = array[min]
+                max -= 1
+                free = min
+            else
+                min += 1
+            end
+        else
+            raise "Invalid state"
+        end
+    end
+
+    array[free] = pivot
+    #Recursive call to quicksort function
+    quicksort array, from_idx, free - 1
+    quicksort array, free + 1, to_idx
+end
+
+#Test for quicksort implementation
+a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15].shuffle
+quicksort a
+puts "quicksort"
+print a