Linked List

Author: piyush-eon

#9 - Linked List/1-linked-list.js

@@ -0,0 +1,135 @@
+// Linked List in Javascript
+
+class Node {
+  constructor(data) {
+    this.data = data;
+    this.next = null;
+  }
+}
+
+class LinkedList {
+  constructor() {
+    this.head = null;
+  }
+
+  addFirst(data) {
+    const newNode = new Node(data);
+    newNode.next = this.head;
+    this.head = newNode;
+  }
+
+  addLast(data) {
+    const newNode = new Node(data);
+
+    if (!this.head) {
+      this.head = newNode;
+      return;
+    }
+
+    let current = this.head;
+    while (current.next) {
+      current = current.next;
+    }
+
+    current.next = newNode;
+  }
+
+  size() {
+    let count = 0;
+    let current = this.head;
+    while (current) {
+      count++;
+      current = current.next;
+    }
+    return count;
+  }
+
+  addAt(index, data) {
+    if (index < 0 || index > this.size()) {
+      console.error("Invalid Index");
+      return;
+    }
+
+    const newNode = new Node(data);
+    if (index === 0) {
+      newNode.next = this.head;
+      this.head = newNode;
+      return;
+    }
+
+    let current = this.head;
+    for (let i = 0; i < index - 1; i++) {
+      current = current.next;
+    }
+
+    newNode.next = current.next;
+    current.next = newNode;
+  }
+
+  removeTop() {
+    if (!this.head) {
+      return;
+    }
+
+    this.head = this.head.next;
+  }
+
+  removeLast() {
+    if (!this.head) {
+      return;
+    }
+
+    let current = this.head;
+    while (current.next.next) {
+      current = current.next;
+    }
+
+    current.next = null;
+  }
+
+  removeAt(index) {
+    if (index < 0 || index > this.size()) {
+      console.error("Invalid Index");
+      return;
+    }
+
+    if (index === 0) {
+      this.head = this.head.next;
+      return;
+    }
+
+    let current = this.head;
+    for (let i = 0; i < index - 1; i++) {
+      current = current.next;
+    }
+
+    if (current.next) {
+      current.next = current.next.next;
+    }
+  }
+
+  print() {
+    let current = this.head;
+    while (current) {
+      console.log(current.data);
+      current = current.next;
+    }
+  }
+}
+
+const linkedlist = new LinkedList();
+
+linkedlist.addFirst(5);
+linkedlist.addFirst(3);
+linkedlist.addFirst(8);
+linkedlist.addLast(6);
+
+linkedlist.removeTop();
+
+linkedlist.addAt(2, 8);
+
+linkedlist.removeLast();
+linkedlist.removeAt(2);
+
+linkedlist.print();
+console.log("size = " + linkedlist.size());

#9 - Linked List/2-palindrome-linked-list.js

@@ -0,0 +1,24 @@
+// Ques 1 : Given the head of a singly linked list, return true if it is
+// a palindrome or false otherwise
+
+// Input: head = [1,2,2,1]      ----->>>>>      Output: true;
+// Input: head = [1,2]          ----->>>>>      Output: false;
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+var isPalindrome = function (head) {
+  let string1 = (string2 = "");
+  let node = head;
+
+  while (node != null) {
+    string1 = `${string1}${node.val}`;
+    string2 = `${node.val}${string2}`;
+    node = node.next;
+  }
+  return string1 === string2;
+};

#9 - Linked List/3-reverse-linked-list.js

@@ -0,0 +1,23 @@
+// Ques 2 : Given the head of a singly linked list, reverse the list, and
+// return the reversed list.
+
+// Input: head = [1,2]      ----->>>>>      Output: [2,1];
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+var reverseList = (head) => {
+  let prev = null;
+  let current = head;
+  while (current !== null) {
+    const nextNode = current.next;
+    current.next = prev;
+    prev = current;
+    current = nextNode;
+  }
+  return prev;
+};