feat: Add remove k-th last element (#2)

* feat: Add remove k-th last element from single-linked list.

* Fix filenames.

* Update docs.

Author: goloroden

README.md

@@ -6,6 +6,7 @@ codingcircle contains the examples from the YouTube Coding Cirle.
 
 So far, the following exercises have been covered:
 
+- [Playlist](./playlist/) – removing the k-th last element from a single-linked list
 - [Trie](./trie/) – implementing an autocomplete feature using a trie
 
 ## Running quality assurance

playlist/documentation.go

@@ -0,0 +1,3 @@
+// Package playlist provides a single-linked list where the k-th last element
+// can be removed.
+package playlist

playlist/get_list_values.go

@@ -0,0 +1,13 @@
+package playlist
+
+func GetListValues(head *Node) []int {
+	node := head
+
+	var values []int
+	for node != nil {
+		values = append(values, node.Value)
+		node = node.Next
+	}
+
+	return values
+}

playlist/node.go

@@ -0,0 +1,13 @@
+package playlist
+
+type Node struct {
+	Value int
+	Next  *Node
+}
+
+func NewNode(value int, next *Node) *Node {
+	return &Node{
+		Value: value,
+		Next:  next,
+	}
+}

playlist/remove_kth_last_element.go

@@ -0,0 +1,26 @@
+package playlist
+
+func RemoveKthLastElement(head *Node, k int) *Node {
+	lead := head
+	follow := head
+
+	for i := 0; i < k; i++ {
+		if lead == nil {
+			return nil
+		}
+		lead = lead.Next
+	}
+
+	if lead == nil {
+		return head.Next
+	}
+
+	for lead.Next != nil {
+		lead = lead.Next
+		follow = follow.Next
+	}
+
+	follow.Next = follow.Next.Next
+
+	return head
+}

playlist/remove_kth_last_element_test.go

@@ -0,0 +1,65 @@
+package playlist_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/thenativeweb/codingcircle/playlist"
+)
+
+func TestRemoveKthLastElement(t *testing.T) {
+	t.Run("remove last element", func(t *testing.T) {
+		list :=
+			playlist.NewNode(2,
+				playlist.NewNode(3,
+					playlist.NewNode(5,
+						playlist.NewNode(7,
+							playlist.NewNode(11, nil)))))
+
+		updatedList := playlist.RemoveKthLastElement(list, 1)
+		values := playlist.GetListValues(updatedList)
+
+		assert.Equal(t, []int{2, 3, 5, 7}, values)
+	})
+
+	t.Run("remove first element", func(t *testing.T) {
+		list :=
+			playlist.NewNode(2,
+				playlist.NewNode(3,
+					playlist.NewNode(5,
+						playlist.NewNode(7,
+							playlist.NewNode(11, nil)))))
+
+		updatedList := playlist.RemoveKthLastElement(list, 5)
+		values := playlist.GetListValues(updatedList)
+
+		assert.Equal(t, []int{3, 5, 7, 11}, values)
+	})
+
+	t.Run("remove k-th last element", func(t *testing.T) {
+		list :=
+			playlist.NewNode(2,
+				playlist.NewNode(3,
+					playlist.NewNode(5,
+						playlist.NewNode(7,
+							playlist.NewNode(11, nil)))))
+
+		updatedList := playlist.RemoveKthLastElement(list, 2)
+		values := playlist.GetListValues(updatedList)
+
+		assert.Equal(t, []int{2, 3, 5, 11}, values)
+	})
+
+	t.Run("with too large k", func(t *testing.T) {
+		list :=
+			playlist.NewNode(2,
+				playlist.NewNode(3,
+					playlist.NewNode(5,
+						playlist.NewNode(7,
+							playlist.NewNode(11, nil)))))
+
+		updatedList := playlist.RemoveKthLastElement(list, 17)
+
+		assert.Nil(t, updatedList)
+	})
+}