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 :)
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