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GitHub - zzangu0215/algorithm-practice: This is a repository for practicing algorithm problems to prepare technical interviews.

Table of Contents

Week 1

01-Arithmetic

Q. Write code to create functions capable of different arithmetic operations.

Solution:

const add = function (num1, num2) {
  return num1 + num2;
};

const subtract = function (num1, num2) {
  return num1 - num2;
};

const multiply = function (num1, num2) {
  return num1 * num2;
};

const divide = function (num1, num2) {
  return num1 / num2;
};

02-Odd or Even

Q. Write code to create a function that determines whether a number is odd or even.

Solution:

const oddOrEven = function (num) {
  if (num % 2 === 0) {
    return "even";
  } else {
    return "odd";
  }
};

03-Log Nums

Q. Write code to create a function that prints all whole numbers from 1 to a given number.

Solution:

const logNums = function (num) {
  for (let i = 1; i <= num; i++) {
    console.log(i);
  }
};

Week 2

01-Log Even Nums

Q. Write code to create a function that prints even numbers from 0 to a given number.

Solution #1:

const logEvenNums = function (num) {
  for (let i = 0; i <= num; i++) {
    if (i % 2 === 0) {
      console.log(i);
    }
  }
};

Solution #2:

const logEvenNums = function (num) {
  for (let i = 0; i <= num; i += 2) {
    console.log(i);
  }
};

02-Countdown

Q. Write code to create a function that prints all whole numbers from num to a given number.

Solution:

const countdown = function (num) {
  for (let i = num; i > 0; i--) {
    console.log(i);
  }
};

03-Sum Array

Q. Write code to create a function that adds up all the numbers in a given array and returns the total.

Solution:

const sumArray = function (arr) {
  let result = 0;

  for (let i = 0; i < arr.length; i++) {
    const currentNumber = arr[i];
    result += currentNumber;
  }

  return result;
};

Week 3

01-Fizz Buzz

Q. Write code to create a function that solves the Fizz Buzz problem.

Solution:

const fizzBuzz = function (arr) {
  for (let i = 0; i < arr.length; i++) {
    const currentNumber = arr[i];

    if (currentNumber % 15 === 0) {
      console.log("Fizz Buzz");
    } else if (currentNumber % 3 === 0) {
      console.log("Fizz");
    } else if (currentNumber % 5 === 0) {
      console.log("Buzz");
    } else {
      console.log(currentNumber);
    }
  }
};

02-Max Num

Q. Write code to create a function that returns the largest number present in a given array.

Solution:

const maxNum = function (arr) {
  let max = arr[0];

  for (let i = 1; i < arr.length; i++) {
    const currentNum = arr[i];

    if (currentNum > max) {
      max = currentNum;
    }
  }

  return max;
};

03-Vowel Count

Q. Write code to create a function that counts the number of vowels in a given string.

Solution #1:

const vowelCount = function (str) {
  let result = 0;
  const vowels = ["a", "e", "i", "o", "u"];

  for (let i = 0; i < str.length; i++) {
    const letter = str[i].toLowerCase();

    if (vowels.indexOf(letter) !== -1) {
      result += 1;
    }
  }

  return result;
};

Solution #2:

const vowelCount = function (str) {
  let result = 0;

  for (let i = 0; i < str.length; i++) {
    const letter = str[i].toLowerCase();

    if (
      letter === "a" ||
      letter === "e" ||
      letter === "i" ||
      letter === "o" ||
      letter === "u"
    ) {
      result += 1;
    }
  }

  return result;
};

Week 4

01-Is Palindrome

Q. Write code to create a function that takes in a string and determines whether or not it is a palindrome. A palindrome is any string spelled the same forwards as it is backward.

Solution #1:

const isPalindrome = function (str) {
  const reversedString = str.split("").reverse().join("");

  if (reversedString === str) {
    return true;
  }
  return false;
};

Solution #2:

const isPalindrome = function (str) {
  for (let i = 0; i < str.length; i++) {
    if (str[i] !== str[str.length - 1 - i]) {
      return false;
    }
  }
  return true;
};

02-Factorial

Q. Write code to create a function that returns the factorial of a given number. A factorial of a number is the product of all positive integers less than or equal to the number. For more information, see the Wikipedia page on factorials.

Solution:

const factorial = function (num) {
  let result = 1;

  for (let i = num; i > 1; i--) {
    result *= i;
  }

  return result;
};

03-Title Case

Q. Write code to create a function that capitalizes the first letter of every word in a given string.

Solution:

const titleCase = function (str) {
  const result = [];

  const words = str.split(" ");

  for (let i = 0; i < words.length; i++) {
    const word = words[i].split("");

    word[0] = word[0].toUpperCase();

    result.push(word.join(""));
  }

  return result.join(" ");
};

Week 5

01-Character Count

Q. Write code to create a function that takes a string and returns an object containing the characters in the string and the number of times they appear.

Hint: MDN Web Docs on object bracket notation

Solution:

const characterCount = function (str) {
  const charObject = {};

  for (let i = 0; i < str.length; i++) {
    let char = str[i];

    if (char in charObject) {
      charObject[char]++;
    } else {
      charObject[char] = 1;
    }
  }

  return charObject;
};

02-Product of Largest Two

Q. Write code to create a function that finds the largest two numbers in an array and returns the product of both numbers.

Solution #1:

const productOfLargestTwo = function (arr) {
  const largest = Math.max(...arr);

  const newArr = arr.filter((num) => num < largest);
  const secondLargest = Math.max(...newArr);

  return largest * secondLargest;
};

Solution #2:

var productOfLargestTwo = function (arr) {
  var largest = null;
  var secondLargest = null;

  for (var i = 0; i < arr.length; i++) {
    var currentNumber = arr[i];

    if (currentNumber > largest || largest === null) {
      secondLargest = largest;
      largest = currentNumber;
    } else if (currentNumber > secondLargest || secondLargest === null) {
      secondLargest = currentNumber;
    }
  }

  return largest * secondLargest;
};

03-Camel Case

Q. Write code to create a function that takes a string and returns the string in camel case.

Solution #1:

const camelCase = function (str) {
  const words = str.split(" ");

  const result = words
    .map((word) => {
      return word[0].toUpperCase() + word.slice(1);
    })
    .join("");

  return result[0].toLowerCase() + result.slice(1);
};

Solution #2:

var camelCase = function (str) {
  var result = "";
  var words = str.toLowerCase().split(" ");

  for (var i = 0; i < words.length; i++) {
    var word = words[i];
    var letters = word.split("");

    if (i > 0) {
      letters[0] = letters[0].toUpperCase();
    }

    result += letters.join("");
  }

  return result;
};

Week 6

01-Linear Search

Q. Write code to create a function that takes an array of numbers and a target number and returns the index of the target number in the given array.

Solution:

const linearSearch = (arr, target) => {
  if (target in arr) {
    for (let i = 0; i < arr.length; i++) {
      if (target === arr[i]) return i;
    }
  } else {
    return -1;
  }
};

02-Is Unique

Q. Write code to create a function that takes an array of numbers and returns true if no number appears more than once in the given array; else, it returns false.

Solution:

const isUnique = (arr) => {
  const numOpject = {};

  for (let i = 0; i < arr.length; i++) {
    if (numOpject[arr[i]] === true) return false;

    numOpject[arr[i]] = true;
  }

  return true;
};

03-Is Anagram

Q. Write code to create a function that takes in two strings and return true if one string is an anagram of another string and otherwise returns false.

Note: An anagram is a word or phrase made by rearranging the letters of another word or phrase. See the Wikipedia page on anagrams for more information.

Solution #1:

const isAnagram = (strA, strB) => {
  const strA_Arr = strA.split("").sort();
  const strB_Arr = strB.split("").sort();

  if (strA_Arr.join("") === strB_Arr.join("")) return true;
  else return false;
};

Solution #2:

const isAnagram = (strA, strB) => {
  if (strA.length !== strB.length) {
    return false;
  }

  const aLetterMap = {};
  const bLetterMap = {};
  const strLength = strA.length;

  for (let i = 0; i < strLength; i += 1) {
    const aLetter = strA[i];
    const bLetter = strB[i];

    aLetterMap[aLetter] = (aLetterMap[aLetter] || 0) + 1;
    bLetterMap[bLetter] = (bLetterMap[bLetter] || 0) + 1;
  }

  // Array.prototype.some tests whether at least one element in the array passes
  // the test implemented by the provided function.
  // (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some)
  const hasUnequalLetterCount = Object.keys(aLetterMap).some(
    (key) => aLetterMap[key] !== bLetterMap[key]
  );

  return !hasUnequalLetterCount;
};

Week 7

01-Most Songs in Playlist

Q. Write code to create a function that takes an array of numbers, each representing the duration of a song. You will return the maximum number of songs present in the array that can fit into a 60 minute playlist.

Solution #1:

const mostSongsInPlaylist = function (arr) {
  const sortedArr = arr.sort();
  let totalMins = 0;
  let totalSongs = 0;

  for (let i = 0; i < sortedArr.length; i++) {
    const currentSongDuration = sortedArr[i];

    if (totalMins + currentSongDuration <= 60) {
      totalMins += currentSongDuration;
      totalSongs++;
    } else {
      return totalSongs;
    }
  }

  return totalSongs;
};

Solution #2:

const mostSongsInPlaylist = function (arr) {
  const sortedArr = arr.sort();
  let sum = 0;

  for (let i = 0; i < sortedArr.length; i++) {
    sum += sortedArr[i];

    if (sum > 60) return i;
  }

  return sortedArr.length;
};

02-Is Perfect Square

Q. Write code to create a function that takes in a whole number, and returns true if the number is a perfect square, otherwise returns false.

Solution:

const isPerfectSquare = function (num) {
  let i = 0;

  while (true) {
    if (i * i === num) return true;
    if (i * i > num) return false;
    i++;
  }
};

03-Array Search 2d

Q. Write code to create a function that takes in a 2-dimensional array and searches each 2D element for the character "X".

Solution #1:

const arraySearch2D = function (arr) {
  const newArr = arr.flat();
  let count = 0;

  for (let i = 0; i < newArr.length; i++) {
    if (newArr[i] === "X") count += 1;
  }

  return count;
};

Solution #2:

const arraySearch2D = function (arr) {
  let count = 0;

  for (let i = 0; i < arr.length; i++) {
    for (let k = 0; k < arr[i].length; k++) {
      if (arr[i][k] === "X") {
        count++;
      }
    }
  }

  return count;
};

Week 8

01-Multiply Into 20

Q. Write code to create a function that takes an array of unique numbers. Return true if any two numbers can be multiplied into 20, else return false.

Solution #1:

const multiplyInto20 = function (arr) {
  const temp = arr.filter((num) => 20 % num === 0 && num > 0);

  if (temp.length >= 2) return true;
  else return false;
};

Solution #2:

const multiplyInto20 = function (arr) {
  const numMap = {};

  for (let i = 0; i < arr.length; i++) {
    const currentNum = arr[i];

    const neededNumber = 20 / currentNum;

    if (numMap[neededNumber]) {
      return true;
    }
    numMap[currentNum] = true;
  }

  return false;
};

02-Zeroes and Ones

Q. Write code to create a function that takes in a string containing only 0s and 1s, and returning true if there are an equal number of 0s and 1s, else returning false.

Solution:

const zeroesAndOnes = function (str) {
  let zeroes = 0;
  let ones = 0;

  for (let i = 0; i < str.length; i++) {
    if (str[i] === "0") zeroes++;
    if (str[i] === "1") ones++;
  }

  if (zeroes === ones) return true;
  else return false;
};

03-Merge Sorted

Q. Write code to create a function that takes in two sorted arrays of numbers and merges the contents of both arrays into one new sorted array.

Note: You may not use the built in sort method for this activity.

Solution:

const mergeSorted = (arr1, arr2) => {
  const sortedArr = [];

  let idx1 = 0;
  let idx2 = 0;

  while (idx1 < arr1.length && idx2 < arr2.length) {
    if (arr1[idx1] < arr2[idx2]) {
      sortedArr.push(arr1[idx1]);
      idx1++;
    } else {
      sortedArr.push(arr2[idx2]);
      idx2++;
    }
  }

  while (idx1 < arr1.length) {
    sortedArr.push(arr1[idx1]);
    idx1++;
  }

  while (idx2 < arr2.length) {
    sortedArr.push(arr2[idx2]);
    idx2++;
  }

  return sortedArr;
};

Week 9

01-Double Triple Map

Q. Write code to create a function that takes in an array of integers and returns a transformed array where even numbers are doubled and odd numbers are tripled.

Solution #1:

const doubleTripleMap = function (arr) {
  const newArr = arr.map((num) => {
    if (num % 2 === 0) return num * 2;
    else return num * 3;
  });

  return newArr;
};

Solution #2:

const doubleTripleMap = function (arr) {
  const doubleTripleArr = [];

  for (let i = 0; i < arr.length; i++) {
    const num = arr[i];

    if (num % 2 === 0) {
      doubleTripleArr.push(num * 2);
    } else {
      doubleTripleArr.push(num * 3);
    }
  }
  return doubleTripleArr;
};

02-Array Intersection

Q. Write code to create a function that takes two arrays and returns a new array that is the intersection of both arrays.

Solution #1:

const arrayIntersection = function (arr1, arr2) {
  const newArr = arr1.filter((num) => arr2.includes(num));

  return newArr;
};

Solution #2:

const arrayIntersection = function (arr1, arr2) {
  const numMap = {};
  const result = [];

  for (var i = 0; i < arr1.length; i++) {
    var num = arr1[i];

    if (numMap[num] === undefined) {
      numMap[num] = 1;
    } else {
      numMap[num]++;
    }
  }

  for (var i = 0; i < arr2.length; i++) {
    var num = arr2[i];

    if (numMap[num]) {
      result.push(num);
      numMap[num]--;
    }
  }

  return result;
};

03-Squares of A Sorted Array

Q. Write code to create a function that takes an array of integers sorted in ascending (increasing) order and returns a new array containing the squares of each number in ascending order.

Solution #1:

const sortedSquares = function (arr) {
  const squared = arr.map((num) => num * num);

  return squared.sort((a, b) => {
    return a - b;
  });
};

Solution #2:

const sortedSquares = function (arr) {
  const result = new Array(arr.length);

  let idx1 = 0;
  let idx2 = arr.length - 1;
  let idx3 = result.length - 1;

  while (idx1 <= idx2) {
    const left = arr[idx1];
    const right = arr[idx2];

    if (Math.abs(left) > Math.abs(right)) {
      result[idx3] = left ** 2;
      idx1++;
    } else {
      result[idx3] = right ** 2;
      idx2--;
    }

    idx3--;
  }

  return result;
};

Solution #3:

const sortedSquares = function (arr) {
  const squares = arr.map(function (num) {
    return num ** 2;
  });

  const sortedSquares = squares.sort(function (a, b) {
    return a - b;
  });

  return sortedSquares;
};

Week 10

01-Common Element

Q. Write code to create a function that takes in two arrays of numbers, with one number in common between the two arrays. Your function should return the number in common between the two array.

Solution:

const commonElement = function (arrA, arrB) {
  const elem = {};

  arrA.map((num) => (elem[num] = true));

  for (let i = 0; i < arrB.length; i++) {
    if (elem[arrB[i]] === true) return arrB[i];
  }
};

02-Permutation Substring

Q. Write code to create a function that takes in two strings and returns true if the second string is a substring of any permutation (combination of characters in) the first string.

Solution #1:

const permutationSubstring = function (str, sub) {
  const strArr = str.split("").sort();
  const subArr = sub.split("").sort();

  let count = 0;
  for (let i = 0; i < subArr.length; i++) {
    if (strArr.join("").includes(subArr[i])) count++;
  }

  if (count === subArr.length) return true;
  else return false;
};

Solution #2:

const permutationSubstring = function (str, sub) {
  const charMap = {};

  for (var i = 0; i < str.length; i++) {
    var char = str[i];

    if (char in charMap) {
      charMap[char]++;
    } else {
      charMap[char] = 1;
    }
  }

  for (var i = 0; i < sub.length; i++) {
    var char = sub[i];
    if (!charMap[char]) {
      return false;
    }
    charMap[char] -= 1;
  }

  return true;
};

03-Concert Flyer

Q. Write code to create a function that takes in two strings: a concert flyer and a magazine. You will be checking if the words in the concert flyer could have been clipped from the magazine, e.g. if every instance of each word in the second string is found in the first string, return true, else return false.

Solution #1:

const concertFlyer = function (magazine, flyer) {
  const magWordsArr = magazine.split(" ");
  const flyWordsArr = flyer.split(" ");

  let count = 0;

  for (let i = 0; i < flyWordsArr.length; i++) {
    if (magWordsArr.includes(flyWordsArr[i])) count++;
  }

  if (count === flyWordsArr.length) return true;
  else return false;
};

Solution #2:

const concertFlyer = function (magazine, flyer) {
  const magazineWords = magazine.split(" ");
  const flyerWords = flyer.split(" ");

  const magazineMap = {};
  const flyerMap = {};

  for (var i = 0; i < magazineWords.length; i++) {
    var word = magazineWords[i];
    if (!magazineMap[word]) {
      magazineMap[word] = 1;
    } else {
      magazineMap[word]++;
    }
  }

  for (var i = 0; i < flyerWords.length; i++) {
    var word = flyerWords[i];
    if (!flyerMap[word]) {
      flyerMap[word] = 1;
    } else {
      flyerMap[word]++;
    }
  }

  for (const key in flyerMap) {
    if (magazineMap[key] !== flyerMap[key]) {
      return false;
    }
  }

  return true;
};

Week 11

01-Reverse No Built In

Q. Write code to create a function that takes a given string and returns a new string with all of the characters in reverse order. You are not permitted to use the built-in reverse method.

Solution:

const reverse = (str) => {
  console.log(str);

  let reverse = "";
  for (let i = str.length - 1; i >= 0; i--) {
    reverse += str[i];
  }

  return reverse;
};

02-Left Rotation

Q. Write code to create a function that takes an array of integers and a positive integer as arguments. The function should then rotate the elements of the array to the left by the given number.

Solution:

const leftRotation = (arr, positions) => {
  if (arr.length === 0) return;

  while (positions > 0) {
    const firstElem = arr.shift();

    arr.push(firstElem);

    positions--;
  }
};

03-Reverse In Place

Q. Write code to create a function that takes an array and reverses the array in place without using the built-in reverse method.

Solution #1:

const reverseInPlace = (arr) => {
  const left = 0;
  const right = arr.length - 1;
  const half = right / 2;

  for (let i = 0; i < half; i++) {
    const temp = arr[left + i];
    arr[left + i] = arr[right - i];
    arr[right - i] = temp;
  }

  return arr;
};

Solution #2:

const reverseInPlace = (arr) => {
  let left = 0;
  let right = arr.length - 1;

  while (left < right) {
    const temp = arr[left];
    arr[left] = arr[right];
    arr[right] = temp;

    left++;
    right--;
  }

  return arr;
};

Week 12

01-Valid Brackets

Q. Write code to create a function that takes in a string and returns true if the string contains a valid set or sets of brackets, else false should be returned.

Solution:

const validBrackets = function (str) {
  const stack = [];

  for (let i = 0; i < str.length; i += 1) {
    const char = str[i];

    if (char === "(" || char === "{" || char === "[") {
      stack.push(char);
    } else if (char === ")") {
      if (stack.pop() !== "(") {
        return false;
      }
    } else if (char === "}") {
      if (stack.pop() !== "{") {
        return false;
      }
    } else if (char === "]") {
      if (stack.pop() !== "[") {
        return false;
      }
    }
  }

  return stack.length === 0;
};

02-Min Increment For Unique

Q. Write code to create a function that takes in an array of numbers and returns the minimum number of increments needed to make the numbers unique.

Solution:

const minIncrement = function (nums) {
  const uniqueNums = {};
  let increments = 0;

  for (let i = 0; i < nums.length; i += 1) {
    while (uniqueNums[nums[i]] === true) {
      nums[i] += 1;
      increments += 1;
    }

    uniqueNums[nums[i]] = true;
  }

  return increments;
};

03-Peak Finder

Q. Write code to create a function that takes in an array of numbers and returns the peak of the array.

Solution:

const peakFinder = function (nums) {
  if (nums.length === 1) {
    return nums[0];
  }

  if (nums[0] > nums[1]) {
    return nums[0];
  }

  if (nums[nums.length - 1] > nums[nums.length - 2]) {
    return nums[nums.length - 1];
  }

  let min = 0;
  let max = nums.length - 1;

  while (min < max) {
    const middle = Math.floor((max - min) / 2) + min;

    if (nums[middle - 1] < nums[middle] && nums[middle] > nums[middle + 1]) {
      return nums[middle];
    }

    if (nums[middle - 1] > nums[middle]) {
      max = middle;
    } else {
      min = middle;
    }
  }

  // empty array, return not a number
  return NaN;
};

Week 13

01-Is Armstrong

Q. Write code to create a function that takes a positive integer and returns true if the integer is an armstrong number, else return false. To find out if a number is an armstrong number, take each individual digit and raise it to the power of the length of the entire number and add the digits. If the sum equals the original number, the number is an armstrong number. For more information, refer to the following Quora post: What is an Armstrong Number.

Solution:

const isArmstrong = function (num) {
  const str = String(num);
  let sum = 0;

  for (let i = 0; i < str.length; i++) {
    const digit = parseInt(str[i]);
    sum += digit ** str.length;
  }

  return sum === num;
};

02-Max Profit

Q. Write code to create a function that takes in an array of numbers each representing the price of a stock on a different day. Return the maximum profit that can be made from a single purchase of stock on one day and a single sale on a later day.

Solution:

const maxProfit = function (prices) {
  let smallest = Infinity;
  let bestProfit = 0;

  for (let i = 0; i < prices.length; i++) {
    const price = prices[i];
    smallest = Math.min(smallest, price);
    bestProfit = Math.max(bestProfit, price - smallest);
  }

  return bestProfit;
};

03-Smallest Difference

Q. Write code to create a function that takes in two sorted arrays of integers. Your function should return a new two element array containing one number from each sorted array with the smallest difference.

Solution:

const smallestDifference = function (arr1, arr2) {
  let left = 0;
  let right = 0;
  let bestPair = [];
  let bestDiff = Infinity;

  while (left < arr1.length && right < arr2.length) {
    const leftVal = arr1[left];
    const rightVal = arr2[right];
    const currentDiff = Math.abs(rightVal - leftVal);

    if (currentDiff < bestDiff) {
      bestDiff = currentDiff;
      bestPair = [leftVal, rightVal];

      if (bestDiff === 0) {
        return bestPair;
      }
    }

    if (leftVal < rightVal) {
      left++;
    } else if (rightVal < leftVal) {
      right++;
    }
  }

  return bestPair;
};

Week 14

01-Maximum Continuous Subarray

Q. Write code to create a function that takes in an array and returns the sum of the maximum continuous, or contiguous, subarray.

Note: Contiguous refers to items that are next to each other in sequence. In the array [1, 2, 3, -27, 5], for example, [1, 2, 3] is a contiguous subarray while [1, 2, 3, 5] is not, since 5 is not directly next to 3 in the sequence.

Solution:

const maxSumArray = function (numbers) {
  // If array contains only one integer, return the value as the sum
  if (numbers.length === 1) {
    return numbers[0];
    // If the array contains two integers or only positive integers return the sum
  }
  if (numbers.length === 2 || numbers.every((x) => x >= 0)) {
    return numbers.reduce((a, b) => a + b, 0);
  }
  // Set the current max and max sum to the value of the first integer in array
  let currentMax = numbers[0];
  let maxSum = numbers[0];
  // Loop through array to test for maximum sum
  for (let x = 1; x < numbers.length; x++) {
    let numToTest = numbers[x];
    // Set currentMax to equal either the number to test or sum of number to test and currentMax
    currentMax = Math.max(numToTest, numToTest + currentMax);
    // Set maxSum to be the max of the currentMax or the current maxSum value
    maxSum = Math.max(maxSum, currentMax);
  }
  return maxSum;
};

02-Merge Meeting Times

Q. Write code to create a function that takes in a 2D array of meeting times, with each sub-array containing two integers that represent a meeting's start and end times. Return a new 2D array of collapsed meeting times -- that is, combined sub-arrays where meeting blocks overlap to reflect the combined start and end time.

Solution:

var mergeMeetingTimes = function (arr) {
  var arrCopy = JSON.parse(JSON.stringify(arr));
  var sortedArr = arrCopy.sort((a, b) => a[0] - b[0]);

  var result = [sortedArr[0]];

  for (var i = 1; i < sortedArr.length; i++) {
    var lastMeeting = result[result.length - 1];
    var currentMeeting = sortedArr[i];

    if (lastMeeting[1] >= currentMeeting[0]) {
      if (lastMeeting[1] < currentMeeting[1]) {
        lastMeeting[1] = currentMeeting[1];
      }
    } else {
      result.push(currentMeeting);
    }
  }

  return result;
};

03-Int To Roman

Q. Write code to create a function that takes in an integer and returns a string that represents the number as a Roman numeral. If you aren't familiar with Roman numerals or want to review them, refer to Your Dictionary's Roman Numerals Chart, Translation Tips & History.

Solution:

var intToRoman = function (num) {
  var result = "";

  while (num > 0) {
    if (num >= 1000) {
      result += "M";
      num -= 1000;
    } else if (num >= 900) {
      result += "CM";
      num -= 900;
    } else if (num >= 500) {
      result += "D";
      num -= 500;
    } else if (num >= 400) {
      result += "CD";
      num -= 400;
    } else if (num >= 100) {
      result += "C";
      num -= 100;
    } else if (num >= 90) {
      result += "XC";
      num -= 90;
    } else if (num >= 50) {
      result += "L";
      num -= 50;
    } else if (num >= 40) {
      result += "XL";
      num -= 40;
    } else if (num >= 40) {
      result += "XL";
      num -= 40;
    } else if (num >= 10) {
      result += "X";
      num -= 10;
    } else if (num >= 9) {
      result += "IX";
      num -= 9;
    } else if (num >= 5) {
      result += "V";
      num -= 5;
    } else if (num >= 4) {
      result += "IV";
      num -= 4;
    } else if (num >= 1) {
      result += "I";
      num -= 1;
    }
  }

  return result;
};

Week 15

01-Plus One

Q. Write code to create a function that takes in an array of digits representing a non-negative integer and add 1 to it. The digits are arranged such that the most significant digits are on the left and each element in the array contains a single integer digit.

Solution:

const plusOne = function (digits) {
  let carry = 1;

  for (let i = digits.length - 1; i >= 0; i--) {
    const plusOne = digits[i] + carry;
    var sum;
    carry = 0;

    if (plusOne > 9) {
      carry = 1;
      sum = 10 - plusOne;
    } else {
      sum = plusOne;
    }

    digits[i] = sum;
  }

  if (carry) {
    digits.unshift(carry);
  }

  return digits;
};

02-One Edit Away

Q. Write code to create a function that takes in two strings and returns true if they are exactly one character edit away from each other, else return false.

Solution:

const oneEditAway = function (str1, str2) {
  // If difference in string lengths is greater than 1 OR strings exactly equal, return false
  if (str1 === str2 || Math.abs(str1.length - str2.length) > 1) {
    return false;
  }
  // Initial index for each string is 0
  let index1 = 0;
  let index2 = 0;
  // Set edit count to zero
  let editCount = 0;

  while (index1 < str1.length && index2 < str2.length) {
    // If characters in string are not a match
    if (str1[index1] !== str2[index2]) {
      // Check edit count. If editCount is 1, return false.
      if (editCount === 1) {
        return false;
      }
      // If one string is longer then can only add a character
      if (str1.length > str2.length) {
        index1++;
      } else if (str2.length < str1.length) {
        index2++;
        // If one string is not longer, strings must be equal length
      } else {
        index1++;
        index2++;
      }
      editCount++;
      // If current characters are equal
    } else {
      index1++;
      index2++;
    }
  }
  return true;
};

03-Caesar Cipher

Q. Write code to create a function that takes in a string and an offset integer. Your function should return a new string with characters shifted up by the offset. If you're unfamiliar with Caesar Cipher, spend a few minutes reading over the Wikipedia page on Caesar Cipher.

Solution:

const caesarCipher = function (str, offset) {
  let result = "";

  while (offset < 0) {
    offset = 26 + offset;
  }

  for (let i = 0; i < str.length; i++) {
    const char = str[i];
    const charCode = char.charCodeAt(0);
    let offsetChar = char;

    if (charCode >= 65 && charCode <= 90) {
      offsetChar = String.fromCharCode(((charCode - 65 + offset) % 26) + 65);
    } else if (charCode >= 97 && charCode <= 122) {
      offsetChar = String.fromCharCode(((charCode - 97 + offset) % 26) + 97);
    }

    result += offsetChar;
  }

  return result;
};

Week 16

01-Roman To Int

Q. Write code to create a function that takes in a Roman numeral string and returns its integer form. If you aren't familiar with Roman numerals or would like to review them, refer to this guide to Roman numerals.

Solution:

var romanToInt = function (str) {
  var numerals = {
    I: 1,
    V: 5,
    X: 10,
    L: 50,
    C: 100,
    D: 500,
    M: 1000,
  };

  var result = 0;

  for (var i = 0; i < str.length; i++) {
    var currentNumeral = str[i];
    var nextNumeral = str[i + 1];

    var currentValue = numerals[currentNumeral];
    var nextValue = numerals[nextNumeral];

    if (currentValue < nextValue) {
      result -= currentValue;
    } else {
      result += currentValue;
    }
  }

  return result;
};

02-Rotation Point

Q. Write code to create a function that takes in an array of strings. These strings will be in sorted order, but the array might be rotated. Return the index of the rotation, or -1 if there is none.

Solution:

var rotationPoint = function (words) {
  var left = 0;
  var right = words.length - 1;

  while (left <= right) {
    var middle = Math.floor((right + left) / 2);

    if (words[middle] < words[middle - 1]) {
      return middle;
    }

    if (words[left] > words[middle]) {
      right = middle - 1;
    } else {
      left = middle + 1;
    }
  }

  return -1;
};

03-Simplify Path

Q. Write code to create a function that takes in a string representing an absolute file path and then simplifies it, similar to path.join.

Solution:

var simplifyPath = function (path) {
  var pathArr = path.split("/");
  var stack = [];

  for (var i = 0; i < pathArr.length; i++) {
    var section = pathArr[i];

    if (!section) {
      continue;
    }

    if (section === ".") {
      continue;
    }

    if (section === "..") {
      stack.pop();
      continue;
    }

    stack.push(section);
  }

  return "/" + stack.join("/");
};