Add doubly linked list class and reverse to method singly linked list

Signed-off-by: Darko Draskovic <[email protected]>

src/doubly-linked-list.js

@@ -0,0 +1,122 @@
+export class DoublyLinkedList {
+  constructor(value) {
+    this.head = {
+      value: value,
+      next: null,
+      prev: null,
+    }
+    this.tail = this.head;
+    this.length = 1;
+  }
+  append(value) {
+    this.tail.next = {
+      value: value,
+      next: null,
+      prev: this.tail,
+    },
+    this.tail = this.tail.next;
+    this.length++;
+    return this;
+  }
+  prepend(value) {
+    this.head = {
+      value: value,
+      next: this.head,
+      prev: null,
+    }
+    this.head.next.prev = this.head;
+    this.length++;
+    return this;
+  }
+
+  insert(index, value) {
+    if (index <= 0) return this.prepend(value);
+    if (index >= this.length) return this.append(value);
+
+    const current = this.traverse(index-1);
+    current.next = {
+      value: value,
+      next: current.next,
+      prev: current,
+    }
+    current.next.next.prev = current.next;
+    this.length++;
+    return this;
+  }
+
+  remove(index) {
+    if (index < 0 || index >= this.length) {
+      return;
+    }
+
+    const current = this.traverse(index-1);
+    if (index === 0) {
+      this.head = this.head.next;
+      this.head.prev = null;
+    }    
+    else if (index === this.length-1) {
+      this.tail = current;
+      current.next = null;
+    } else {
+      current.next = current.next.next;
+      current.next.prev = current;
+    }
+    this.length--;
+    return this;
+  }
+
+  traverse(index) {
+    let current = this.head;
+    if (index >= 0) {
+      for (let i = 0; i < index; i++) {
+        current = current.next;
+      }
+    } else {
+      current = this.tail;
+      for (let i = this.length-1; i > this.length+index; i--) {
+        current = current.prev;
+      }
+    }
+    return current;
+  }
+
+  array() {
+    const arr = [];
+    let current = this.head;
+    while (current !== null) {
+      arr.push(current.value);
+      current = current.next;
+    }
+    return arr;
+  }
+}
+
+export function test() {
+  const linkedList = new DoublyLinkedList(0);
+  linkedList.append(1);
+  linkedList.append(2);
+  linkedList.append(3);
+  linkedList.append(4);
+  console.log(linkedList.array());
+  console.log(linkedList.traverse(-1).value);
+  console.log(linkedList.traverse(-3).value);
+  console.log(linkedList.traverse(-linkedList.length).value);
+
+  linkedList.remove(0);
+  console.log(linkedList.array());
+  console.log(linkedList.traverse(-linkedList.length).value);
+  linkedList.remove(1);
+  console.log(linkedList.array());
+  console.log(linkedList.traverse(-linkedList.length).value);
+  linkedList.remove(linkedList.length-1);
+  console.log(linkedList.array());
+  console.log(linkedList.traverse(-linkedList.length).value);
+
+  linkedList.insert(1, 0);
+  console.log(linkedList.array());
+  console.log(linkedList.traverse(-linkedList.length).value);
+
+  linkedList.prepend(-1);
+  console.log(linkedList.array());
+  console.log(linkedList.traverse(-linkedList.length).value);
+}

src/linked-list.js

@@ -74,6 +74,22 @@ export class LinkedList {
     }
     return arr;
   }
+
+  reverse() {
+    let current = this.head;
+    let next = current.next;
+    this.head.next = null;
+    this.head = this.tail;
+
+    while(next) {
+      const tmp = next.next;
+      next.next = current;
+      current = next;
+      next = tmp;
+    }
+    this.head = current;
+    return this;
+  }
 }
 
 export function test() {
@@ -101,4 +117,7 @@ export function test() {
   linkedList.remove(linkedList.length-1);
   linkedList.remove(linkedList.length);
   console.log(linkedList.array());
+
+  linkedList.reverse();
+  console.log(linkedList.array());
 }