diff --git a/Data-Structures/Linked-List/SinglyLinkedList.js b/Data-Structures/Linked-List/SinglyLinkedList.js
index 605ede4013..ec0e31f5fc 100644
--- a/Data-Structures/Linked-List/SinglyLinkedList.js
+++ b/Data-Structures/Linked-List/SinglyLinkedList.js
@@ -1,10 +1,10 @@
/* SinglyLinkedList!!
-* A linked list is similar to an array, it holds a list of values.
-* However, links in a linked list do not have indexes. With
-* a linked list you do not need to predetermine its size as
-* it grows and shrinks as it is edited. This is an example of
-* a singly linked list.
-*/
+ * A linked list is similar to an array, it holds a list of values.
+ * However, links in a linked list do not have indexes. With
+ * a linked list you do not need to predetermine its size as
+ * it grows and shrinks as it is edited. This is an example of
+ * a singly linked list.
+ */
// Methods - size, head, addLast, addFirst, addAt, removeFirst, removeLast, remove, removeAt, indexOf, isEmpty, elementAt, findMiddle, get, clean, rotateListRight
@@ -18,6 +18,7 @@ class Node {
class LinkedList {
constructor (listOfValues) {
this.headNode = null
+ this.tailNode = null
this.length = 0
if (listOfValues instanceof Array) {
@@ -42,6 +43,11 @@ class LinkedList {
return this.headNode?.data || null
}
+ // Returns the tail
+ tail () {
+ return this.tailNode?.data || null
+ }
+
// Return if the list is empty
isEmpty () {
return this.length === 0
@@ -53,16 +59,10 @@ class LinkedList {
if (this.headNode === null) {
return this.addFirst(element)
}
- let { currentNode } = this.initiateNodeAndIndex()
-
- // Loop till there is a node present in the list
- while (currentNode.next) {
- currentNode = currentNode.next
- }
-
const node = new Node(element)
// Adding node at the end of the list and increase the length
- currentNode.next = node
+ this.tailNode.next = node
+ this.tailNode = node
this.length++
return this.size()
}
@@ -70,6 +70,11 @@ class LinkedList {
// add a node at first it to linklist
addFirst (element) {
const node = new Node(element)
+ // Check if its the first element
+ if (this.headNode === null) {
+ this.tailNode = node
+ }
+ // Adding node at the start of the list and increase the length
node.next = this.headNode
this.headNode = node
this.length++
@@ -78,10 +83,17 @@ class LinkedList {
// remove the first from the linklist
removeFirst () {
+ // Check if head is null
+ if (this.headNode === null) {
+ return null
+ }
+ // Removing node at the start of the list and decrease the length
const removedNode = this.headNode
- if (this.length > 0) {
- this.headNode = this.headNode.next
- this.length--
+ this.headNode = this.headNode.next
+ this.length--
+ // Check if the list is empty
+ if (this.isEmpty()) {
+ this.tailNode = null
}
return removedNode?.data
}
@@ -89,16 +101,18 @@ class LinkedList {
// remove the last from the linklist
removeLast () {
if (this.isEmpty()) return null
+ // Check if there is only one element
if (this.length === 1) {
return this.removeFirst()
}
- let { currentIndex, currentNode } = this.initiateNodeAndIndex()
- while (currentIndex !== this.length - 2) {
- currentIndex++
+ // Removing node at the end of the list and decrease the length
+ const removedNode = this.tailNode
+ let { currentNode } = this.initiateNodeAndIndex()
+ while (currentNode.next.next) {
currentNode = currentNode.next
}
- const removedNode = currentNode.next
currentNode.next = null
+ this.tailNode = currentNode
this.length--
return removedNode.data
}
@@ -112,13 +126,17 @@ class LinkedList {
if (currentNode.data === element) {
return this.removeFirst()
}
+ // Check if the tail node is the element to remove
+ if (this.tailNode.data === element) {
+ return this.removeLast()
+ }
// Check which node is the node to remove
- while (currentNode?.next) {
+ while (currentNode.next) {
if (currentNode.next.data === element) {
removedNode = currentNode.next
currentNode.next = currentNode.next.next
this.length--
- break
+ return removedNode.data
}
currentNode = currentNode.next
}
@@ -127,10 +145,9 @@ class LinkedList {
// Returns the index of the element passed as param otherwise -1
indexOf (element) {
- let { currentIndex, currentNode } = this.initiateNodeAndIndex()
-
+ if (this.isEmpty()) return -1
+ let { currentNode, currentIndex } = this.initiateNodeAndIndex()
while (currentNode) {
- // Checking if the node is the element we are searching for
if (currentNode.data === element) {
return currentIndex
}
@@ -185,7 +202,7 @@ class LinkedList {
throw new RangeError('Out of Range index')
}
if (index === 0) return this.removeFirst()
- if (index === this.length) return this.removeLast()
+ if (index === this.length - 1) return this.removeLast()
let { currentIndex, currentNode } = this.initiateNodeAndIndex()
while (currentIndex !== index - 1) {
@@ -194,7 +211,6 @@ class LinkedList {
}
const removedNode = currentNode.next
currentNode.next = currentNode.next.next
- // Decrementing the length
this.length--
return removedNode.data
}
@@ -215,6 +231,7 @@ class LinkedList {
// make the linkedList Empty
clean () {
this.headNode = null
+ this.tailNode = null
this.length = 0
}
@@ -226,34 +243,28 @@ class LinkedList {
list.push(currentNode.data)
currentNode = currentNode.next
}
-
return list
}
// Method for Rotating a List to the right by k places
rotateListRight (k) {
- let i = 0
+ if (!this.headNode) return
let current = this.headNode
- while (current) {
- i++
+ let tail = this.tailNode
+ let count = 1
+ while (current.next) {
+ count++
current = current.next
}
- k %= i
- current = this.headNode
- let prev = null
- while (k--) {
- if (!current || !current.next) {
- return current
- } else {
- while (current.next) {
- prev = current
- current = current.next
- }
- prev.next = current.next
- current.next = this.headNode
- this.headNode = current
- }
+ current.next = this.headNode
+ tail = current
+ k %= count
+ while (count - k > 0) {
+ tail = tail.next
+ count--
}
+ this.headNode = tail.next
+ tail.next = null
}
// Method to iterate over the LinkedList
@@ -286,6 +297,7 @@ class LinkedList {
prev = head
head = next
}
+ this.tailNode = this.headNode
this.headNode = prev
};
}
diff --git a/Data-Structures/Linked-List/test/SinglyLinkedList.test.js b/Data-Structures/Linked-List/test/SinglyLinkedList.test.js
index a04d06ba15..5435553437 100644
--- a/Data-Structures/Linked-List/test/SinglyLinkedList.test.js
+++ b/Data-Structures/Linked-List/test/SinglyLinkedList.test.js
@@ -150,6 +150,20 @@ describe('SinglyLinkedList', () => {
expect(list.head()).toBe(30)
})
+ it('Check tail', () => {
+ const list = new LinkedList()
+ expect(list.tail()).toBe(null)
+
+ list.addLast(10)
+ expect(list.tail()).toBe(10)
+
+ list.addLast(20)
+ expect(list.tail()).toBe(20)
+
+ list.addFirst(30)
+ expect(list.tail()).toBe(20)
+ })
+
it('Check size', () => {
const list = new LinkedList()
expect(list.size()).toBe(0)
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