Circular linked list

Directions

Given a linked list, return true if the list is circular, false if it is not.

Examples#

const l = new List();const a = new Node('a');const b = new Node('b');const c = new Node('c');l.head = a;a.next = b;b.next = c;c.next = b;circular(l) // trueconst l = new List();
const a = new Node('a');
const b = new Node('b');
const c = new Node('c');
l.head = a;
a.next = b;
b.next = c;
c.next = b;
circular(l) // true

Try it first#

Copy the stub, make the 4 tests pass on your machine, then open the solution. The reveal is remembered per page in this browser.

JSexercises/circular/index.js

function circular(list) {} module.exports = circular;function circular(list) {}

module.exports = circular;

Solution#

JScompleted_exercises/circular/index.js

function circular(list) {  let slow = list.getFirst();  let fast = list.getFirst();   while (fast.next && fast.next.next) {    slow = slow.next;    fast = fast.next.next;     if (slow === fast) {      return true;    }  }   return false;} module.exports = circular;function circular(list) {
  let slow = list.getFirst();
  let fast = list.getFirst();

  while (fast.next && fast.next.next) {
    slow = slow.next;
    fast = fast.next.next;

    if (slow === fast) {
      return true;
    }
  }

  return false;
}

module.exports = circular;
const circular = require('./index');const L = require('./linkedlist');const List = L.LinkedList;const Node = L.Node; test('circular', () => {  expect(typeof circular).toEqual('function');}); test('circular detects circular linked lists', () => {  const l = new List();  const a = new Node('a');  const b = new Node('b');  const c = new Node('c');   l.head = a;  a.next = b;  b.next = c;  c.next = b;   expect(circular(l)).toEqual(true);}); test('circular detects circular linked lists linked at the head', () => {  const l = new List();  const a = new Node('a');  const b = new Node('b');  const c = new Node('c');   l.head = a;  a.next = b;  b.next = c;  c.next = a;   expect(circular(l)).toEqual(true);}); test('circular detects non-circular linked lists', () => {  const l = new List();  const a = new Node('a');  const b = new Node('b');  const c = new Node('c');   l.head = a;  a.next = b;  b.next = c;  c.next = null;   expect(circular(l)).toEqual(false);}); const circular = require('./index');
const L = require('./linkedlist');
const List = L.LinkedList;
const Node = L.Node;

test('circular', () => {
  expect(typeof circular).toEqual('function');
});

test('circular detects circular linked lists', () => {
  const l = new List();
  const a = new Node('a');
  const b = new Node('b');
  const c = new Node('c');

  l.head = a;
  a.next = b;
  b.next = c;
  c.next = b;

  expect(circular(l)).toEqual(true);
});

test('circular detects circular linked lists linked at the head', () => {
  const l = new List();
  const a = new Node('a');
  const b = new Node('b');
  const c = new Node('c');

  l.head = a;
  a.next = b;
  b.next = c;
  c.next = a;

  expect(circular(l)).toEqual(true);
});

test('circular detects non-circular linked lists', () => {
  const l = new List();
  const a = new Node('a');
  const b = new Node('b');
  const c = new Node('c');

  l.head = a;
  a.next = b;
  b.next = c;
  c.next = null;

  expect(circular(l)).toEqual(false);
});
class Node {  constructor(data, next = null) {    this.data = data;    this.next = next;  }} class LinkedList {  constructor(values = []) {    this.head = null;     for (let value of values) {      this.insertLast(value);    }  }   clear() {    this.head = null;  }   size() {    let counter = 0;    let node = this.head;     while (node) {      counter++;      node = node.next;    }     return counter;  }   getAt(index) {    if (!this.head) {      return null;    }     let counter = 0;    let node = this.head;    while (node) {      if (counter === index) {        return node;      }      node = node.next;      counter++;    }    return null;  }   insertAt(data, index) {    if (!this.head) {      this.head = new Node(data);      return;    }     if (index === 0) {      this.head = new Node(data, this.head);      return;    }     let counter = 1;    let previous = this.head;    let node = this.head.next;    while (node) {      if (counter === index) {        previous.next = new Node(data, node);        return;      }      previous = node;      node = node.next;      counter++;    }     previous.next = new Node(data, node);  }   removeFirst() {    if (!this.head) {      return;    }     this.head = this.head.next;  }   removeLast() {    if (!this.head) {      return;    }     if (!this.head.next) {      this.head = null;      return;    }     let previous = this.head;    let node = this.head.next;    while (node.next) {      previous = node;      node = node.next;    }    previous.next = null;  }   removeAt(index) {    if (!this.head) {      return;    }     let counter = 0;    let node = this.head;    while (node) {      if (counter === index - 1) {        if (node.next) {          return (node.next = node.next.next);        } else {          return (node.next = null);        }      }      node = node.next;      counter++;    }  }   getFirst() {    return this.head;  }   insertFirst(data) {    this.head = new Node(data, this.getFirst());  }   getLast() {    if (!this.head) {      return null;    }     let node = this.head;    while (node.next) {      node = node.next;    }     return node;  }   insertLast(data) {    const last = this.getLast();     if (last) {      last.next = new Node(data);      return last.next;    } else {      this.head = new Node(data);      return this.head;    }  }   forEach(fn) {    if (!this.head) {      return null;    }     let node = this.head;    while (node) {      fn(node);      node = node.next;    }  }   *[Symbol.iterator]() {    let node = this.head;    while (node) {      yield node;      node = node.next;    }  }} module.exports = { Node, LinkedList }; class Node {
  constructor(data, next = null) {
    this.data = data;
    this.next = next;
  }
}

class LinkedList {
  constructor(values = []) {
    this.head = null;

    for (let value of values) {
      this.insertLast(value);
    }
  }

  clear() {
    this.head = null;
  }

  size() {
    let counter = 0;
    let node = this.head;

    while (node) {
      counter++;
      node = node.next;
    }

    return counter;
  }

  getAt(index) {
    if (!this.head) {
      return null;
    }

    let counter = 0;
    let node = this.head;
    while (node) {
      if (counter === index) {
        return node;
      }
      node = node.next;
      counter++;
    }
    return null;
  }

  insertAt(data, index) {
    if (!this.head) {
      this.head = new Node(data);
      return;
    }

    if (index === 0) {
      this.head = new Node(data, this.head);
      return;
    }

    let counter = 1;
    let previous = this.head;
    let node = this.head.next;
    while (node) {
      if (counter === index) {
        previous.next = new Node(data, node);
        return;
      }
      previous = node;
      node = node.next;
      counter++;
    }

    previous.next = new Node(data, node);
  }

  removeFirst() {
    if (!this.head) {
      return;
    }

    this.head = this.head.next;
  }

  removeLast() {
    if (!this.head) {
      return;
    }

    if (!this.head.next) {
      this.head = null;
      return;
    }

    let previous = this.head;
    let node = this.head.next;
    while (node.next) {
      previous = node;
      node = node.next;
    }
    previous.next = null;
  }

  removeAt(index) {
    if (!this.head) {
      return;
    }

    let counter = 0;
    let node = this.head;
    while (node) {
      if (counter === index - 1) {
        if (node.next) {
          return (node.next = node.next.next);
        } else {
          return (node.next = null);
        }
      }
      node = node.next;
      counter++;
    }
  }

  getFirst() {
    return this.head;
  }

  insertFirst(data) {
    this.head = new Node(data, this.getFirst());
  }

  getLast() {
    if (!this.head) {
      return null;
    }

    let node = this.head;
    while (node.next) {
      node = node.next;
    }

    return node;
  }

  insertLast(data) {
    const last = this.getLast();

    if (last) {
      last.next = new Node(data);
      return last.next;
    } else {
      this.head = new Node(data);
      return this.head;
    }
  }

  forEach(fn) {
    if (!this.head) {
      return null;
    }

    let node = this.head;
    while (node) {
      fn(node);
      node = node.next;
    }
  }

  *[Symbol.iterator]() {
    let node = this.head;
    while (node) {
      yield node;
      node = node.next;
    }
  }
}

module.exports = { Node, LinkedList };

Verbatim from the repo at 30cf7634. Alternate tabs are the commented-out solutions with the leading // removed and nothing else changed. Run the tests locally with npx jest circular inside the fork.

Directions

Examples#

Try it first#

Solution#hide again

Solution#