JavaScript exercises: Functions

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Write a function that takes an array of numbers as input and returns the sum of the squares of all the odd numbers in the array.

function sumOfSquaresOfOdds(arr) {
  return arr.filter(num => num % 2 !== 0).reduce((acc, num) => acc + num ** 2, 0);
}

// Example usage
const nums = [1, 2, 3, 4, 5];
console.log(sumOfSquaresOfOdds(nums)); // Output: 35

Write a function that takes two arrays of strings as input, and returns an array containing all the strings that appear in both input arrays.

function commonStrings(arr1, arr2) {
  const set1 = new Set(arr1);
  const set2 = new Set(arr2);
  const common = [];

  set1.forEach(str => {
    if (set2.has(str)) {
      common.push(str);
    }
  });

  return common;
}

// Example usage
const arr1 = ['apple', 'banana', 'orange'];
const arr2 = ['banana', 'kiwi', 'orange'];
console.log(commonStrings(arr1, arr2)); // Output: ['banana', 'orange']

Write a function that takes a string as input and returns the most common letter in the string. If there is a tie for the most common letter, the function should return an array of all the tied letters.

function mostCommonLetter(str) {
  const letterCount = {};

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

    if (/\w/.test(char)) {
      letterCount[char] = (letterCount[char] || 0) + 1;
    }
  }

  const maxCount = Math.max(...Object.values(letterCount));
  const mostCommon = Object.keys(letterCount).filter(key => letterCount[key] === maxCount);

  return mostCommon.length === 1 ? mostCommon[0] : mostCommon;
}

// Example usage
const str = 'hello world';
console.log(mostCommonLetter(str)); // Output: 'l'

Write a function that takes an array of numbers as input and returns the median value of the numbers in the array.

function median(arr) {
  const sorted = arr.sort((a, b) => a - b);
  const mid = Math.floor(sorted.length / 2);

  return sorted.length % 2 !== 0 ? sorted[mid] : (sorted[mid - 1] + sorted[mid]) / 2;
}

// Example usage
const nums = [1, 3, 2, 5, 4];
console.log(median(nums)); // Output: 3

Write a function that takes a string as input and returns a new string with the first letter of each word capitalized, and all other letters lowercase.

function capitalizeWords(str) {
  return str.split(' ').map(word => word.charAt(0).toUpperCase() + word.slice(1).toLowerCase()).join(' ');
}

// Example usage
const str = 'the quick brown fox';
console.log(capitalizeWords(str)); // Output: 'The Quick Brown Fox'

Write a function that takes an array of objects as input, where each object represents a person with a name and an age, and returns the name of the oldest person in the array.

function oldestPerson(people) {
  const oldest = people.reduce((acc, person) => person.age > acc.age ? person : acc, people[0]);
  return oldest.name;
}

// Example usage
const people = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 30 },
  { name: 'Charlie', age: 20 }
];
console.log(oldestPerson(people)); // Output: 'Bob'

Write a function that takes a string as input and returns true if the string is a palindrome (reads the same forwards and backwards), and false otherwise.

function factorial(num) {
  if (num === 0) {
    return 1;
  } else {
    return num * factorial(num - 1);
  }
}

// Example usage
console.log(factorial(5)); // Output: 120

Write a function that takes an array of numbers as input and returns the number of unique values in the array.

function isPalindrome(str) {
  const len = str.length;

  for (let i = 0; i < Math.floor(len / 2); i++) {
    if (str[i] !== str[len - 1 - i]) {
      return false;
    }
  }

  return true;
}

// Example usage
console.log(isPalindrome('racecar')); // Output: true

Write a function that takes a string as input and returns the longest word in the string.

function gcd(num1, num2) {
  if (num2 === 0) {
    return num1;
  } else {
    return gcd(num2, num1 % num2);
  }
}

// Example usage
console.log(gcd(12, 18)); // Output: 6

Write a function that takes an array of numbers as input and returns an array containing all the unique pairs of numbers that add up to a specified target value.

function removeDuplicates(arr) {
  return arr.filter((item, index) => arr.indexOf(item) === index);
}

// Example usage
const nums = [1, 2, 3, 2, 4, 3];
console.log(removeDuplicates(nums)); // Output: [1, 2, 3, 4]

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