class LinkedList {
  constructor() {
    this.nodes = [];
  }

  get size() {
    return this.nodes.length;
  }

  get head() {
    return this.size ? this.nodes[0] : null;
  }

  get tail() {
    return this.size ? this.nodes[this.size - 1] : null;
  }

  insertAt(index, value) {
    const previousNode = this.nodes[index - 1] || null;
    const nextNode = this.nodes[index] || null;
    const node = { value, next: nextNode };

    if (previousNode) previousNode.next = node;
    this.nodes.splice(index, 0, node);
  }

  insertFirst(value) {
    this.insertAt(0, value);
  }

  insertLast(value) {
    this.insertAt(this.size, value);
  }

  getAt(index) {
    return this.nodes[index];
  }

  removeAt(index) {
    const previousNode = this.nodes[index - 1];
    const nextNode = this.nodes[index + 1] || null;

    if (previousNode) previousNode.next = nextNode;

    return this.nodes.splice(index, 1);
  }

  clear() {
    this.nodes = [];
  }

  reverse() {
    this.nodes = this.nodes.reduce(
      (acc, { value }) => [{ value, next: acc[0] || null }, ...acc],
      []
    );
  }

  *[Symbol.iterator]() {
    yield* this.nodes;
  }
}

const list = new LinkedList();

list.insertFirst(1);
list.insertFirst(2);
list.insertFirst(3);
list.insertLast(4);
list.insertAt(3, 5);

list.size;                      // 5
list.head.value;                // 3
list.head.next.value;           // 2
list.tail.value;                // 4
[...list.map(e => e.value)];    // [3, 2, 1, 5, 4]

list.removeAt(1);               // 2
list.getAt(1).value;            // 1
list.head.next.value;           // 1
[...list.map(e => e.value)];    // [3, 1, 5, 4]

list.reverse();
[...list.map(e => e.value)];    // [4, 5, 1, 3]

list.clear();
list.size;                      // 0

const binomialCoefficient = (n, k) => {
  if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
  if (k < 0 || k > n) return 0;
  if (k === 0 || k === n) return 1;
  if (k === 1 || k === n - 1) return n;
  if (n - k < k) k = n - k;
  let res = n;
  for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
  return Math.round(res);
};

binomialCoefficient(8, 2); // 28

const euclideanDistance = (a, b) =>
  Math.hypot(...Object.keys(a).map(k => b[k] - a[k]));
  
euclideanDistance([1, 1], [2, 3]); // ~2.2361
euclideanDistance([1, 1, 1], [2, 3, 2]); // ~2.4495

function printHeap(heap, index, level) {
    if (index >= heap.length) {
        return;
    }
    console.log("  ".repeat(level) + heap[index]);
    printHeap(heap, 2 * index + 1, level + 1);
    printHeap(heap, 2 * index + 2, level + 1);
}

//You can call this function by passing in the heap array and the index of the root node, which is typically 0, and level = 0.

let heap = [3, 8, 7, 15, 17, 30, 35, 2, 4, 5, 9];
printHeap(heap,0,0)

const deepMerge = (a, b, fn) =>
  [...new Set([...Object.keys(a), ...Object.keys(b)])].reduce(
    (acc, key) => ({ ...acc, [key]: fn(key, a[key], b[key]) }),
    {}
  );
  
deepMerge(
  { a: true, b: { c: [1, 2, 3] } },
  { a: false, b: { d: [1, 2, 3] } },
  (key, a, b) => (key === 'a' ? a && b : Object.assign({}, a, b))
);
// { a: false, b: { c: [ 1, 2, 3 ], d: [ 1, 2, 3 ] } }

const nums = [1, 2, 3];
const strs = Array.from('est');

nums.push(6);
nums.push(4, 9);
strs.unshift('t');

nums.length;                     // 6
nums[nums.length - 1];           // 9
strs[0];                         // 't'
strs[2];                         // 's'

nums.slice(1, 3);                // [2, 3]
nums.map(n => n * 2);            // [2, 4, 6, 12, 8, 18]
nums.filter(n => n % 2 === 0);   // [2, 6, 4]
nums.reduce((a, n) => a + n, 0); // 25

strs.reverse();                  // ['t', 's', 'e', 't']
strs.join('');                   // 'test'

const nums = new Set([1, 2, 3]);

nums.add(4);
nums.add(1);
nums.add(5);
nums.add(4);

nums.size;                       // 5
nums.has(4);                     // true

nums.delete(4);
nums.has(4);                     // false

[...nums];                       // [1, 2, 3, 5]

nums.clear();
nums.size;                       // 0

const items = new Map([
  [1, { name: 'John' }],
  [2, { name: 'Mary' }]
]);

items.set(4, { name: 'Alan' });
items.set(2, { name: 'Jeff' });

items.size;                      // 3
items.has(4);                    // true
items.get(2);                    // { name: 'Jeff' }

items.delete(2);
items.size;                      // 2

[...items.keys()];               // [1, 4]
[...items.values()];             // [{ name: 'John' }, { name: 'Alan' }]

items.clear();
items.size;                      // 0