JavaScript Data Structures: Singly Linked List: Set

Intro

Last time, we learned how to get a specific node by its index.

Today, we learn how to update / set a specific node.

Current Code

We start with the code after we added get(), because we can use our get method to get the node we want to change.

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

class SinglyLinkedList {
  constructor() {
    this.length = 0;
    this.head = null;
    this.tail = null;
  }

  push(value) {
    const newNode = new Node(value);
    if (this.length > 0) {
      this.tail.next = newNode;
    } else {
      this.head = newNode;
    }
    this.tail = newNode;
    this.length += 1;
    return newNode;
  }

  get(index) {
    if (index < 0 || index >= this.length) {
      return null;
    } else {
      let currentNode = this.head;
      let count = 0;

      while (count < index) {
        currentNode = currentNode.next;
        count += 1;
      }

      return currentNode;
    }
  }
}

Thoughts

First, we should think about the constraints and possibilities:

Because we will use our get method to get the node, this is straight-forward:

get the node at the desired index
if the node does exist, set its value to the desired new value and return it
if the node does not exist, return null

Implementation (Short version, DRY)

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

class SinglyLinkedList {
  constructor() {
    this.length = 0;
    this.head = null;
    this.tail = null;
  }

  push(value) {
    const newNode = new Node(value);
    if (this.length > 0) {
      this.tail.next = newNode;
    } else {
      this.head = newNode;
    }
    this.tail = newNode;
    this.length += 1;
    return newNode;
  }

  get(index) {
    if (index < 0 || index >= this.length) {
      return null;
    } else {
      let currentNode = this.head;
      let count = 0;

      while (count < index) {
        currentNode = currentNode.next;
        count += 1;
      }

      return currentNode;
    }
  }

  set(index, value) {
    // get the node at the desired index
    const currentNode = this.get(index);
    // if the node does exist
    if (currentNode) {
      // set its value to the desired new value
      currentNode.value = value;
      // and return it
      return currentNode;
    } else {
      // if the node does not exist, return null
      return null;
    }
  }
}

Result

Let's have a look how to use the Singly Linked List's set method and its results.

const newSLL = new SinglyLinkedList();
// show List, should be empty
console.log(newSLL);
// SinglyLinkedList { length: 0, head: null, tail: null }

// change a node that does not exist => return null and the empty List
console.log(newSLL.set(0, "new 0"));
// null
console.log(newSLL);
// SinglyLinkedList { length: 0, head: null, tail: null }

// add two nodes and updated both => return updated nodes and show updated List
newSLL.push("0");
newSLL.push("1");
console.log(newSLL.set(0, "new 0")); // Node { value: 'new 0', next: Node { value: '1', next: null } }
console.log(newSLL.set(1, "new 1")); // Node { value: 'new 1', next: null }
console.log(newSLL);
// SinglyLinkedList {
//   length: 2,
//   head: Node { value: 'new 0', next: Node { value: 'new 1', next: null } },
//   tail: Node { value: 'new 1', next: null }
// }

Next Part

We will implement how to insert a new node at a specific index. If you want to be notified, subscribe :)

Blog