JavaScript Interview Questions

has_pair_with_sum.js

// Google Interview Video: https://www.youtube.com/watch?v=XKu_SEDAykw
// Provided an array of numbers,
// find a pair of numbers that add up
// to a provided sum

// O(n) linear time complexity
const hasPairWithSum = (arr, sum) => {
  const set = new Set();            // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
  const len = arr.length;           // Setting the arr.length to a variable here will prevent creating the variable for every iteration in the array
  for (let i = 0; i < len; i++) {
    if (set.has(arr[i])) {          // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/has
      return true;
    }
    set.add(sum - arr[i]);        // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/add
  }
  return false;
}

reverse_integer.js

/**
Given a 32-bit signed integer, reverse digits of an integer.

Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1].
For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
*/

const reverse = (int) => {
  let intString = int.toString()
  if (intString[0] === '-') {
    intString = `${intString}-`
  }
  const reversedInt = parseInt(intString.split('').reverse().join(''), 10)
  return (reversedInt > (2**31 - 1) || reversedInt < -(2**31))
    ? 0
    : reversedInt
}

reverse(123) // 321
reverse(1534236469) // 0
reverse(-1223) // -3221

roman_to_hash.js

/**
Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

    I can be placed before V (5) and X (10) to make 4 and 9. 
    X can be placed before L (50) and C (100) to make 40 and 90. 
    C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
*/

const romanToInt = (romanStr) => {
//   filter param datatype
//   filter unrecognized characters
  const romanHash = {
    'I': 1,
    'V': 5,
    'X': 10,
    'L': 50,
    'C': 100,
    'D': 500,
    'M': 1000
  }
  return romanStr.split('').reduce((acc, roman, i, arr) => {
    const int = romanHash[roman]
    const nextInt = romanHash[arr[i + 1]]
    if (nextInt > int) {
      acc -= int
    } else {
      acc += int
    }
    return acc
  }, 0)
}

romanToInt('MCMXCIV') // 1994

// Solution details: https://leetcode.com/submissions/detail/375386949/

singly_linked_list.js

class LinkedList {
  constructor(value) {
      this.head = {
          value: value,
          next: null
      };
      this.tail = this.head;
      this.length = 1;
  }
  append(value) {
    const newNode = {
      value: value,
      next: null
    }
    console.log(newNode)
    this.tail.next = newNode;
    this.tail = newNode;
    this.length++;
    return this;
  }
  prepend(value) {
    const newNode = {
      value: value,
      next: null
    }
    newNode.next = this.head;
    this.head = newNode;
    this.length++;
    return this;
  }
  printList() {
    const array = [];
    let currentNode = this.head;
    while(currentNode !== null){
        array.push(currentNode.value)
        currentNode = currentNode.next
    }
    return array;
  }
  insert(index, value){
    //Check for proper parameters;
    if(index >= this.length) {
      console.log('yes')
      return this.append(value);
    }
    
    const newNode = {
      value: value,
      next: null
    }
    const leader = this.traverseToIndex(index-1);
    const holdingPointer = leader.next;
    leader.next = newNode;
    newNode.next = holdingPointer;
    this.length++;
    return this.printList();
  }
  traverseToIndex(index) {
    //Check parameters
    let counter = 0;
    let currentNode = this.head;
    while(counter !== index){
      currentNode = currentNode.next;
      counter++;
    }
    return currentNode;
  }
  remove(index) {
    // Check Parameters      
    const leader = this.traverseToIndex(index-1);
    const unwantedNode = leader.next;
    leader.next = unwantedNode.next;
    this.length--;
    return this.printList();
  }
  reverse() {
    //Code Here
    if (this.length <= 1) {
      return this.printList()
    }
    let firstNode = this.head
    this.tail = this.head
    let secondNode = firstNode.next
    while (secondNode) {
      let tempNode = secondNode.next;
      secondNode.next = firstNode
      firstNode = secondNode
      secondNode = tempNode
    }
    this.head.next = null;
    this.head = firstNode;
    return this.printList();
  }
}

let myLinkedList = new LinkedList(10);
myLinkedList.append(5)
myLinkedList.append(16)
myLinkedList.prepend(1)
myLinkedList.printList()
myLinkedList.insert(2, 99)
myLinkedList.insert(20, 88)
myLinkedList.printList()
myLinkedList.remove(2)
myLinkedList.reverse()