From 77540e759f97b05ff53b14c252f3aa65064a1e74 Mon Sep 17 00:00:00 2001
From: Matheus Alves <malvgomes@gmail.com>
Date: Wed, 23 Oct 2019 23:24:40 -0300
Subject: [PATCH] Adding cocktail sort implementation

---
 array/sort/cocktail_sort/Readme.md            | 27 ++++++++++++
 array/sort/cocktail_sort/cocktail_sort.go     | 24 +++++++++++
 .../sort/cocktail_sort/cocktail_sort_test.go  | 42 +++++++++++++++++++
 3 files changed, 93 insertions(+)
 create mode 100644 array/sort/cocktail_sort/Readme.md
 create mode 100644 array/sort/cocktail_sort/cocktail_sort.go
 create mode 100644 array/sort/cocktail_sort/cocktail_sort_test.go

diff --git a/array/sort/cocktail_sort/Readme.md b/array/sort/cocktail_sort/Readme.md
new file mode 100644
index 0000000..6518792
--- /dev/null
+++ b/array/sort/cocktail_sort/Readme.md
@@ -0,0 +1,27 @@
+# Cocktail Sort
+It is a sorting algorithm that iterates over an array in both directions, leaving the largest elements to the right, and the lowest elements to the left. It is a variation of the Bubble Sort Algorithm.
+
+### Example
+[1, 4, 5, 3, 2]
+
+1) <b>1</b> 4 5 3 2
+2) 1 <b>4</b> 5 3 2
+3) 1 4 <b>3</b> 5 2
+4) 1 4 3 <b>2</b> 5
+5) 1 4 3 2 <b>5</b>
+5) 1 4 2 <b>3</b> 5
+6) 1 2 <b>4</b> 3 5
+6) 1 <b>2</b> 4 3 5
+7) <b>1</b> 2 4 3 5
+8) 1 <b>2</b> 4 3 5
+9) 1 2 <b>3</b> 4 5
+10) 1 2 3 <b>4</b> 5
+11) 1 2 3 4 <b>5</b>
+
+And then, the array is sorted.
+
+```
+Best case (When it is already sorted): O(n)
+Worst case: O(n^2)
+Average time complexity: O(n^2)
+```
diff --git a/array/sort/cocktail_sort/cocktail_sort.go b/array/sort/cocktail_sort/cocktail_sort.go
new file mode 100644
index 0000000..9d4be07
--- /dev/null
+++ b/array/sort/cocktail_sort/cocktail_sort.go
@@ -0,0 +1,24 @@
+package sort
+
+func CocktailSort(arr []int) []int {
+	swapped := true
+	for swapped {
+		swapped = false
+		for i := 0; i < len(arr)-1; i++ {
+			if arr[i] > arr[i+1] {
+				arr[i], arr[i+1] = arr[i+1], arr[i]
+				swapped = true
+			}
+		}
+		if !swapped {
+			break
+		}
+		for i := len(arr) - 1; i > 0; i-- {
+			if arr[i] < arr[i-1] {
+				arr[i], arr[i-1] = arr[i-1], arr[i]
+				swapped = true
+			}
+		}
+	}
+	return arr
+}
diff --git a/array/sort/cocktail_sort/cocktail_sort_test.go b/array/sort/cocktail_sort/cocktail_sort_test.go
new file mode 100644
index 0000000..d3e4f55
--- /dev/null
+++ b/array/sort/cocktail_sort/cocktail_sort_test.go
@@ -0,0 +1,42 @@
+package sort
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCocktailSort(t *testing.T) {
+	tests := []struct {
+		name  string
+		arr   []int
+		valid []int
+	}{
+		{
+			"Unsorted array",
+			[]int{5, 3, 2, 1, 8, 4},
+			[]int{1, 2, 3, 4, 5, 8},
+		},
+		{
+			"Sorted array",
+			[]int{1, 2, 3, 4, 5, 6},
+			[]int{1, 2, 3, 4, 5, 6},
+		},
+		{
+			"Equal values",
+			[]int{5, 5, 5, 5, 5, 5},
+			[]int{5, 5, 5, 5, 5, 5},
+		},
+		{
+			"Sorted and reversed",
+			[]int{6, 5, 4, 3, 2, 1},
+			[]int{1, 2, 3, 4, 5, 6},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			assert.Equal(t, test.valid, CocktailSort(test.arr))
+		})
+	}
+}