stathw-js-cheatsheet Cheat Sheet

A Programming › JavaScript cheat sheet in English by username1

This is a cheatsheet for the homeworks of the Statistics course of the MSc in Cybersecurity @ Sapienza. It contains Javascript code snippets for the most useful data structures.

Statistics Homework

2,764 views 845 downloads 16 Oct 2023 History

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Array

Declaration and initialization let array = ['cyber', 'insecurity', 'sapienza'];
let also = new Array(3);

Adding an element
array[3] = 'statistics';

Setting a value
array[1] = 'security';

Deleting an element
delete array[3];

Looping
array.forEach(function(item) {
console.log(item);
});

Checking the existence of a value #1
array.includes('cyber');

Checking the existence of a value #2
array.indexOf('statistics') !== -1;

Checking the existence of a value #3
for (let i = 0; i < array.length; i++) {
if (array[i] === searchValue) {
found = true;
break;
}
}

Checking the existence of a value #4
array.find(item => item === searchValue) !== undefined;

Arrays are also used to implement List, Queue, Stack. For these data structures I'll create a JS class that exposes useful methods.

LinkedList

Creation
let linkedList = new LinkedList();

Adding an element
linkedList.append(3);
linkedList.prepend(1);
linkedList.addAt(1, 3);

Fetch of the head value
linkedList.fetchHead();

Get the value of a node
linkedList.getAt(2);

Removing an element
linkedList.removeAt(1);
linkedList.delete(7);

Check existence of a value
linkedList.contains(7);

Looping
for (const element of linkedList) {
console.log(element);
}

List

Creation
const list = new List();

Adding an element
list.add(1);
list.addAtHead(0);

Removing an element
list.remove(2);

Setting a value
list.set(0, 1337);

Checking existence of a value
list.contains(1);

Looping
for(let i = 0; i < list.size(); i++){
console.log(list.get(i));
});

The type SortedList has the same methods, but ensures that the values are sorted.

Dictionary

Creation
let dict = new Dictionary();

Adding an key-value pair
dict.add('frequency', 20);

Setting a value for a key
dict.set('percentage', 40.10);

Removing a key
dict.remove('percentage');

Checking existence of a key
dict.hasKey('frequency');

Checking existence of a value
dict.hasValue(20);

HashSet

Creation
let hashset = new HashSet();

Adding an element
hashset.add(1);

Removing an element
hashset.delete(1);

Checking the existence of an element
hashset.has(3);

Looping
let keys = hashset.values();
for(let i = 0; i < keys.length; i++){
console.log(keys[i]);
});

The HashSet is pretty similar to the Dictionary, but it doesn't have values; it just uses the keys.

Queue

Creation
let queue = new Queue();

Adding an element
queue.enqueue(1);

Fetch of the first element
queue.front();

Removing an element
queue.dequeue();

Checking the existence of an element
queue.contains(7);

Stack

Creation
let stack = new Stack();

Adding an element
stack.push(1);

Fetching top of stack
stack.peek();

Removing an element
stack.pop();

SortedSet

Creation
let sortedSet = new SortedSet();

Adding an element
sortedSet.add(3);

Removing an element
sortedSet.delete(3);

Checking the existence of an element
sortedSet.has(1);

Looping
for(element in sortedSet.toArray) {
console.log(element);
});

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