implemented linked list, basic testing

src/lib/LinkedList/ListNode.ts

@@ -14,6 +14,10 @@ export default class ListNode<T> extends Node<T> {
         this.next = node;
     }
 
+    setPreviousNode(node: ListNode<T>) {
+        this.prev = node;
+    }
+
     get nextNode() {
         return this.next;
     }

src/lib/LinkedList/index.ts

@@ -0,0 +1,180 @@
+import ListNode from "./ListNode";
+
+export default class LinkedList<T> {
+    private head: ListNode<T> | null
+    private tail: ListNode<T> | null
+
+    constructor(head?: ListNode<T>, tail?: ListNode<T>) {
+        this.head = head || null;
+        this.tail = tail || null;
+    }
+
+    getHead() {
+        return this.head;
+    }
+
+    getTail() {
+        return this.tail;
+    }
+
+    exchange(prev: ListNode<T>, next: ListNode<T>) {
+        prev.setNextNode(next);
+        next.setPreviousNode(prev);
+    }
+
+    addToHead(data: T) {
+        // create a new node for the data to insert, and store the current head
+        const newHead = new ListNode(data);
+        const current = this.head;
+
+        // swap the positions of these elements if current head is defined
+        if (current) this.exchange(current, newHead);
+
+        // assign the new head in the class instance
+        this.head = newHead;
+
+        // if there is no tail after this change, additionally assign the new head as the new tail
+        if (!this.tail) this.tail = newHead;
+    }
+
+    addManyToHead(...items: T[]) {
+        for (let each of items) {
+            this.addToHead(each);
+        }
+    }
+
+    // inverse of the logic above
+    addToTail(data: T) {
+        const newTail = new ListNode(data);
+        const current = this.tail;
+
+        if (current) this.exchange(current, newTail);
+
+        this.tail = newTail;
+        if (!this.head) this.head = newTail;
+    }
+
+    removeHead(): T | null {
+        const toRemove = this.head;
+
+        // if there's nothing to remove, don't remove it
+        if (!toRemove) return null;
+
+        const newHead = toRemove.nextNode;
+        this.head = newHead;
+
+        if (toRemove == this.tail) {
+            this.removeTail();
+        }
+
+        return toRemove.data as T;
+    }
+
+    removeTail(): T | null {
+        const toRemove = this.tail;
+        if (!toRemove) return null;
+
+        const newTail = toRemove.nextNode;
+        this.tail = newTail;
+
+        if (toRemove == this.head) {
+            this.removeHead();
+        }
+
+        return toRemove.data as T;
+    }
+
+    findByNode(node: ListNode<T>): ListNode<T> | null {
+        let current = this.head;
+        while (current !== null) {
+            if (current === node) {
+                return current;
+            }
+
+            current = current.nextNode;
+        }
+
+        return null;
+    }
+
+    findByData(data: T): ListNode<T> | null {
+        let current = this.head;
+        while (current !== null) {
+            if (current.data === data) {
+                return current;
+            }
+
+            current = current.nextNode;
+        }
+
+        return null;
+    }
+
+    removeByData(data: T): ListNode<T> | null {
+        let targetNode: ListNode<T> | null = null;
+        let current = this.head;
+        while (current !== null) {
+            if (current.data == data) {
+                targetNode = current;
+                break;
+            }
+
+            current = current.nextNode;
+        }
+
+        if (!targetNode) return null;
+
+        // by asserting above that target node is neither undefined, nor the head,
+        // nor the tail of the list, we can assert that next and prev will both be
+        // defined, as targetNode must be somewhere in the middle of the list
+        if (targetNode === this.head) {
+            this.removeHead();
+        } else if (targetNode === this.tail) {
+            this.removeTail();
+        } else {
+            // the method below effectively cuts the target node out of the list by assigning
+            // is surrounding members to fill in the space previously taken up by target node
+            const next = targetNode.nextNode;
+            const prev = targetNode.prevNode;
+            this.exchange(prev!, next!);
+        }
+
+        return targetNode;
+    }
+
+    removeAtPosition(pos: number): ListNode<T> | null {
+        let targetNode: ListNode<T> | null = null;
+        let current = this.head;
+        let i = 0;
+
+        // traverse the list until you reach the end or the desired position,
+        // whichever happens first
+        while (current !== null) {
+            if (i == pos) {
+                targetNode = current;
+                break;
+            }
+            current = current.nextNode;
+            i++;
+        }
+
+        // if you arrive at the end of the list without reaching the desired position,
+        // the removal operation was unsuccessful (no element at this position)
+        if (!targetNode && (i < pos)) {
+            console.log("No element found at position " + pos);
+            return null;
+        }
+
+        if (targetNode === this.head) {
+            this.removeHead();
+        } else if (targetNode === this.tail) {
+            this.removeTail();
+        } else {
+            let next = targetNode?.nextNode;
+            let prev = targetNode?.prevNode;
+            this.exchange(prev!, next!);
+        }
+
+        return targetNode;
+    }
+}

src/lib/helpers/sample.ts

@@ -1,9 +1,7 @@
-import Event from "../Event";
-import Graph from "../Graph/Graph";
-import GraphNode from "../Graph/GraphNode";
 import { ChordQuality, EventData } from "./index";
+import LinkedList from "../LinkedList/index";
 
-const initialData: EventData = {
+const firstEvent: EventData = {
     root: "C",
     quality: ChordQuality.Major,
     duration: 4,
@@ -17,17 +15,19 @@ const secondEvent: EventData = {
     beatStrength: "Strong"
 }
 
-const sampleEvent = new Event(initialData);
-const nextEvent = new Event(secondEvent);
-const third = new Event(initialData);
-const fourth = new Event(secondEvent);
+const thirdEvent: EventData = {
+    root: "F",
+    quality: ChordQuality.Major,
+    duration: 4,
+    beatStrength: "Strong"
+}
 
-third.setNextNode(fourth);
-nextEvent.setNextNode(third);
-sampleEvent.setNextNode(nextEvent);
-
-console.log(sampleEvent.getEventData());
-console.log(sampleEvent.nextNode);
+const fourthEvent: EventData = {
+    root: "F",
+    quality: ChordQuality.Minor,
+    duration: 4,
+    beatStrength: "Strong"
+}
 
 /***************
  ***************
@@ -40,14 +40,9 @@ console.log(sampleEvent.nextNode);
  ***************
 ***************/
 
+const eventlist = new LinkedList<EventData>();
+eventlist.addManyToHead(firstEvent, secondEvent, thirdEvent, fourthEvent);
 
-const sampleGraph = new Graph<EventData>(false, false);
+console.log(eventlist);
 
-const pointA = new GraphNode(initialData);
-const pointB = new GraphNode(secondEvent);
-
-sampleGraph.addPoints(pointA, pointB);
-
-sampleGraph.print();
-
-export default {sampleEvent, sampleGraph};
+export default { eventlist }

src/main.ts

@@ -1,10 +1,7 @@
 import data from "./lib/helpers/sample";
+const { eventlist } = data;
 
-const { sampleEvent, sampleGraph } = data;
-const content = JSON.stringify(sampleEvent.getEventData());
-console.log(sampleGraph.print());
-
-export default content;
+// export default content;
 
 // const parser = new DOMParser();
 // const document = parser.parseFromString(content, 'text/html');