Techletter #26 | May 20, 2023
As BFS is based on queue let’s first understand how to implement a queue in JavaScript
// program to implement a queue data structure
class Queue {
constructor() {
this.queue = [];
}
enqueue(element) { // add element
return this.queue.push(element);
}
dequeue() {
if(this.queue.length > 0) {
return this.queue.shift(); // remove first element
}
}
peek() {
return this.queue[this.queue.length - 1];
}
size(){
return this.queue.length;
}
isEmpty() {
return this.queue.length == 0;
}
clear(){
this.queue = [];
}
}
let counter = new Queue();
// add
counter.enqueue(1);
counter.enqueue(2);
counter.enqueue(3);
// get last element
console.log(counter.peek()); // 3
// remove
console.log(counter.dequeue()); // 1
console.log(counter.dequeue()); // 2
console.log(counter.isEmpty()); // false
console.log(counter.size()); // 1
counter.clear();
console.log(counter.size()); // 0
The above code helps you implement a queue. And helps you understand enqueue and deque.
I expect that you already understand JavaScript and are comfortable coding in it. So, I am not explaining the above code line by line.
Now let’s implement and understand BFS implementation.
class Node {
constructor(value) {
this.value = value;
this.neighbors = [];
}
addNeightbors(neighbor) {
this.neighbors.push(neighbor);
}
}
The above class represents a node, where each node has a value and an array of neighbors.\
function bfs(startNode) {
const queue = [];
const visited = new Set();
queue.push(startNode);
visited.add(startNode);
while (queue.length > 0) {
const currentNode = queue.shift()
// print the visited node
console.log(currentNode);
for (let i = 0; i < currentNode.neighbors.length; i++) {
const neighbor = currentNode.neighbors[i];
if (!visited.has(neighbor)) {
queue.push(neighbor);
visited.add(neighbor);
}
}
}
}
If you walk through the above code multiple times you will understand the code, as there is not much complexity in it.