Elevating Array and String Operations in JavaScript

///Sort Numbers by the Number of Divisors
function sortNumbersByDivisors(numbers) {
 function getDivisorCount(num) {
 let count = 0;
 for (let i = 1; i <= num; i++) {
 if (num % i === 0) {
 count++;
 }
 }
 return count;
 }
 return numbers.sort((a, b) => getDivisorCount(a) - getDivisorCount(b));
}
console.log(sortNumbersByDivisors([10, 7, 9, 6])); // Output: [7, 9, 6, 10]

///Replace Every n-th Value in an Array
function replaceNthValue(arr, n, newValue) {
 for (let i = n - 1; i < arr.length; i += n) {
 arr[i] = newValue;
 }
 return arr;
}
console.log(replaceNthValue([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3, 'a')); // Output: [1, 2, 'a', 4, 5, 'a', 7, 8, 'a', 10]

///Check for Consecutive Numbers
function hasThreeConsecutive(arr) {
 for (let i = 0; i < arr.length - 2; i++) {
 if (arr[i] + 1 === arr[i + 1] && arr[i] + 2 === arr[i + 2]) {
 return true;
 }
 }
 return false;
}
console.log(hasThreeConsecutive([1, 2, 3, 5, 8])); // Output: true
console.log(hasThreeConsecutive([1, 2, 4, 5, 7])); // Output: false

///Find Median of Two Sorted Arrays
function findMedianSortedArrays(nums1, nums2) {
 const merged = [...nums1, ...nums2].sort((a, b) => a - b);
 const midIndex = Math.floor(merged.length / 2);
 if (merged.length % 2 === 0) {
 return (merged[midIndex - 1] + merged[midIndex]) / 2;
 } else {
 return merged[midIndex];
 }
}
console.log(findMedianSortedArrays([1, 3], [2])); // Output: 2
console.log(findMedianSortedArrays([1, 2], [3, 4])); // Output: 2.5

///Rotate String
function isRotation(s1, s2) {
 if (s1.length !== s2.length) {
 return false;
 }
 return (s1 + s1).includes(s2);
}
console.log(isRotation("abcde", "deabc")); // Output: true
console.log(isRotation("abcde", "edcba")); // Output: false

///Convert Numeric Score to Letter Grade
function scoreToGrade(score) {
 if (score >= 90) return 'A';
 else if (score >= 80) return 'B';
 else if (score >= 70) return 'C';
 else if (score >= 60) return 'D';
 else return 'F';
}
console.log(scoreToGrade(88)); // Output: 'B'
console.log(scoreToGrade(52)); // Output: 'F'

///Remove Duplicates from Sorted Array
function removeDuplicates(nums) {
 let i = 0;
 for (let j = 1; j < nums.length; j++) {
 if (nums[j] !== nums[i]) {
 i++;
 nums[i] = nums[j];
 }
 }
 return i + 1; // Return the length of the array with unique elements
}
console.log(removeDuplicates([1, 1, 2])); // Output: 2, Array becomes [1, 2]

///Validate Subsequence
function isValidSubsequence(array, sequence) {
 let seqIndex = 0;
 for (let value of array) {
 if (seqIndex === sequence.length) break;
 if (sequence[seqIndex] === value) seqIndex++;
 }
 return seqIndex === sequence.length;
}
console.log(isValidSubsequence([5, 1, 22, 25, 6, -1, 8, 10], [1, 6, -1, 10])); // Output: true
/// Binary Search
function binarySearch(arr, target) {
 let left = 0;
 let right = arr.length - 1;
 while (left <= right) {
 let mid = Math.floor((left + right) / 2);
 if (arr[mid] === target) {
 return mid;
 } else if (arr[mid] < target) {
 left = mid + 1;
 } else {
 right = mid - 1;
 }
 }
 return -1; // If target is not found
}
console.log(binarySearch([1, 2, 3, 4, 5], 3)); // Output: 2

///Find All Numbers Disappeared in an Array
function findDisappearedNumbers(nums) {
 let n = nums.length;
 let result = [];
 let set = new Set(nums); // Use a set for quick lookup
 for (let i = 1; i <= n; i++) {
 if (!set.has(i)) {
 result.push(i);
 }
 }
 return result;
}
console.log(findDisappearedNumbers([4, 3, 2, 7, 8, 2, 3, 1])); // Output: [5, 6]

///Calculate the Number of Islands
function numIslands(grid) {
 function dfs(row, col) {
 if (row < 0 || col < 0 || row >= grid.length || col >= grid[0].length || grid[row][col] === '0') {
 return;
 }
 grid[row][col] = '0'; // Mark the visited land
 dfs(row + 1, col); // Down
 dfs(row - 1, col); // Up
 dfs(row, col + 1); // Right
 dfs(row, col - 1); // Left
 }
 let count = 0;
 for (let i = 0; i < grid.length; i++) {
 for (let j = 0; j < grid[i].length; j++) {
 if (grid[i][j] === '1') {
 dfs(i, j);
 count++;
 }
 }
 }
 return count;
}
console.log(numIslands([
 ["1","1","0","0","0"],
 ["1","1","0","0","0"],
 ["0","0","1","0","0"],
 ["0","0","0","1","1"]
])); // Output: 3

/// Calculate Average of Numbers in Array
function calculateAverage(nums) {
 return nums.reduce((acc, curr) => acc + curr, 0) / nums.length;
}
console.log(calculateAverage([10, 20, 30, 40, 50])); // Output: 30

///Identify All Prime Numbers Up to n
function listPrimes(n) {
 let primes = [];
 for (let i = 2; i <= n; i++) {
 let isPrime = true;
 for (let j = 2; j <= Math.sqrt(i); j++) {
 if (i % j === 0) {
 isPrime = false;
 break;
 }
 }
 if (isPrime) primes.push(i);
 }
 return primes;
}
console.log(listPrimes(29)); // Output: [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]

///Return Longest Word in String
function findLongestWord(str) {
 let words = str.split(' ');
 return words.reduce((longest, current) => current.length > longest.length ? current : longest);
}
console.log(findLongestWord("The quick brown fox jumped over the lazy dog")); // Output: "jumped"

///Sum of All Odd Fibonacci Numbers
function sumOddFibonacci(n) {
 let a = 1, b = 1;
 let sum = a + b; // Start with first two Fibonacci numbers
 while (b <= n) {
 let nextFib = a + b;
 a = b;
 b = nextFib;
 if (b % 2 !== 0 && b <= n) {
 sum += b;
 }
 }
 return sum;
}
console.log(sumOddFibonacci(10)); // Output: 10 (1 + 1 + 3 + 5)