#frequently asked questions

1. 1. Reverse a String
   1function reverseString(str) {
   2    // Method 1: Using array methods
   3    return str.split('').reverse().join('');
   4    
   5    // Method 2: Using loop
   6    // let reversed = '';
   7    // for(let i = str.length - 1; i >= 0; i--) {
   8    //     reversed += str[i];
   9    // }
   10    // return reversed;
   11}
   12reverseString("Chombi"); // Output: "ibmoCh"
   13

2. 2. Find the Factorial of a Number
   1function factorial(n) {
   2    // Method 1: Using recursion
   3    if (n === 0 || n === 1) return 1;
   4    return n * factorial(n - 1);
   5    
   6    // Method 2: Using loop
   7    // let result = 1;
   8    // for(let i = 2; i <= n; i++) {
   9    //     result *= i;
   10    // }
   11    // return result;
   12}
   13factorial(5); // Output: 120
   14

3. 3. Check if String is Palindrome
   1function isPalindrome(str) {
   2    // Remove non-alphanumeric characters and convert to lowercase
   3    str = str.replace(/[^a-zA-Z0-9]/g, '').toLowerCase();
   4    
   5    // Method 1: Using array methods
   6    return str === str.split('').reverse().join('');
   7    
   8    // Method 2: Using two pointers
   9    // let left = 0;
   10    // let right = str.length - 1;
   11    // while(left < right) {
   12    //     if(str[left] !== str[right]) return false;
   13    //     left++;
   14    //     right--;
   15    // }
   16    // return true;
   17}
   18isPalindrome("A man, a plan, a canal: Panama"); // Output: true
   19

4. 4. Find the Fibonacci Sequence
   1function fibonacci(n) {
   2    // Method 1: Using recursion
   3    if (n <= 1) return n;
   4    return fibonacci(n - 1) + fibonacci(n - 2);
   5    
   6    // Method 2: Using loop (more efficient)
   7    // if (n <= 1) return n;
   8    // let prev = 0, curr = 1;
   9    // for(let i = 2; i <= n; i++) {
   10    //     let next = prev + curr;
   11    //     prev = curr;
   12    //     curr = next;
   13    // }
   14    // return curr;
   15}
   16fibonacci(6); // Output: 8 (sequence: 0,1,1,2,3,5,8)
   17

5. 5. Find Missing Number in Array
   1function findMissingNumber(arr) {
   2    // Method 1: Using sum formula
   3    const n = arr.length + 1;
   4    const expectedSum = (n * (n + 1)) / 2;
   5    const actualSum = arr.reduce((sum, num) => sum + num, 0);
   6    return expectedSum - actualSum;
   7    
   8    // Method 2: Using XOR
   9    // let xor = 0;
   10    // for(let i = 1; i <= arr.length + 1; i++) xor ^= i;
   11    // for(let num of arr) xor ^= num;
   12    // return xor;
   13}
   14findMissingNumber([1,2,4,5]); // Output: 3
   15

6. 6. Remove Duplicates from a String
   1function removeDuplicates(str) {
   2    // Method 1: Using Set
   3    return [...new Set(str)].join('');
   4    
   5    // Method 2: Using object to track seen characters
   6    // let result = '';
   7    // const seen = {};
   8    // for(let char of str) {
   9    //     if(!seen[char]) {
   10    //         result += char;
   11    //         seen[char] = true;
   12    //     }
   13    // }
   14    // return result;
   15}
   16removeDuplicates("hello"); // Output: "helo"

7. 7. Find the First Non-Repeating Character
   1function firstNonRepeatingChar(str) {
   2    // Create frequency map
   3    const charCount = {};
   4    for(let char of str) {
   5        charCount[char] = (charCount[char] || 0) + 1;
   6    }
   7    
   8    // Find first character with count 1
   9    for(let char of str) {
   10        if(charCount[char] === 1) {
   11            return char;
   12        }
   13    }
   14    return null;
   15}
   16firstNonRepeatingChar("leetcode"); // Output: "l"

8. 8. Count the Occurrences of Each Character
   1function countCharacters(str) {
   2    const charCount = {};
   3    for(let char of str) {
   4        charCount[char] = (charCount[char] || 0) + 1;
   5    }
   6    return charCount;
   7}
   8countCharacters("hello"); // Output: { h: 1, e: 1, l: 2, o: 1 }

9. 9. Reverse Words in a Sentence
   1function reverseWords(str) {
   2    // Method 1: Using built-in methods
   3    return str.split(' ').reverse().join(' ');
   4    
   5    // Method 2: Manual implementation
   6    // let words = [];
   7    // let word = '';
   8    // for(let char of str) {
   9    //     if(char === ' ') {
   10    //         words.unshift(word);
   11    //         word = '';
   12    //     } else {
   13    //         word += char;
   14    //     }
   15    // }
   16    // words.unshift(word);
   17    // return words.join(' ');
   18}
   19reverseWords("Hello World"); // Output: "World Hello"

10. 10. Check if Two Strings are Anagrams
    1function areAnagrams(str1, str2) {
    2    // Remove spaces and convert to lowercase
    3    str1 = str1.replace(/s/g, '').toLowerCase();
    4    str2 = str2.replace(/s/g, '').toLowerCase();
    5    
    6    // Method 1: Sort and compare
    7    return str1.split('').sort().join('') === str2.split('').sort().join('');
    8    
    9    // Method 2: Character frequency comparison
    10    // if(str1.length !== str2.length) return false;
    11    // const charCount = {};
    12    // for(let char of str1) {
    13    //     charCount[char] = (charCount[char] || 0) + 1;
    14    // }
    15    // for(let char of str2) {
    16    //     if(!charCount[char]) return false;
    17    //     charCount[char]--;
    18    // }
    19    // return true;
    20}
    21areAnagrams("listen", "silent"); // Output: true

11. 11. Find the Longest Substring Without Repeating Characters
    1function longestSubstringWithoutRepeating(str) {
    2    let maxLength = 0;
    3    let start = 0;
    4    const charMap = new Map();
    5    
    6    for(let end = 0; end < str.length; end++) {
    7        if(charMap.has(str[end])) {
    8            start = Math.max(start, charMap.get(str[end]) + 1);
    9        }
    10        charMap.set(str[end], end);
    11        maxLength = Math.max(maxLength, end - start + 1);
    12    }
    13    return maxLength;
    14}
    15longestSubstringWithoutRepeating("abcabcbb"); // Output: 3

12. 12. Convert a String to an Integer (atoi Implementation)
    1function myAtoi(str) {
    2    const INT_MAX = 2147483647;
    3    const INT_MIN = -2147483648;
    4    
    5    // Remove leading whitespace
    6    str = str.trim();
    7    if(!str) return 0;
    8    
    9    let i = 0;
    10    let sign = 1;
    11    let result = 0;
    12    
    13    // Handle sign
    14    if(str[i] === '+' || str[i] === '-') {
    15        sign = str[i] === '+' ? 1 : -1;
    16        i++;
    17    }
    18    
    19    // Process digits
    20    while(i < str.length && /\d/.test(str[i])) {
    21        result = result * 10 + (str[i] - '0');
    22        if(sign === 1 && result > INT_MAX) return INT_MAX;
    23        if(sign === -1 && -result < INT_MIN) return INT_MIN;
    24        i++;
    25    }
    26    
    27    return sign * result;
    28}
    29myAtoi("42"); // Output: 42
    30myAtoi("   -42"); // Output: -42

13. 13. Compress a String (Run-Length Encoding)
    1function compressString(str) {
    2    if(!str) return "";
    3    
    4    let result = "";
    5    let count = 1;
    6    let currentChar = str[0];
    7    
    8    for(let i = 1; i <= str.length; i++) {
    9        if(str[i] === currentChar) {
    10            count++;
    11        } else {
    12            result += currentChar + count;
    13            currentChar = str[i];
    14            count = 1;
    15        }
    16    }
    17    
    18    return result.length < str.length ? result : str;
    19}
    20compressString("aabbbcccc"); // Output: "a2b3c4"

14. 14. Find the Most Frequent Character
    1function findMostFrequentChar(str) {
    2    const charCount = {};
    3    let maxChar = '';
    4    let maxCount = 0;
    5    
    6    // Count character frequencies
    7    for(let char of str) {
    8        charCount[char] = (charCount[char] || 0) + 1;
    9        if(charCount[char] > maxCount) {
    10            maxChar = char;
    11            maxCount = charCount[char];
    12        }
    13    }
    14    return maxChar;
    15}
    16findMostFrequentChar("hello world"); // Output: "l"

15. 15. Find All Substrings of a Given String
    1function findAllSubstrings(str) {
    2    const substrings = [];
    3    
    4    // Generate all possible substrings
    5    for(let i = 0; i < str.length; i++) {
    6        for(let j = i + 1; j <= str.length; j++) {
    7            substrings.push(str.slice(i, j));
    8        }
    9    }
    10    return substrings;
    11}
    12findAllSubstrings("abc"); // Output: ["a", "ab", "abc", "b", "bc", "c"]

16. 16. Check if a String is a Rotation of Another String
    1function isRotation(str1, str2) {
    2    // Check if lengths are equal and not empty
    3    if(str1.length !== str2.length || !str1.length) return false;
    4    
    5    // Concatenate str1 with itself and check if str2 is substring
    6    return (str1 + str1).includes(str2);
    7}
    8isRotation("hello", "llohe"); // Output: true
    9isRotation("hello", "world"); // Output: false

17. 17. Remove All White Spaces from a String
    1function removeWhitespace(str) {
    2    // Method 1: Using regex
    3    return str.replace(/\s/g, '');
    4    
    5    // Method 2: Using split and join
    6    // return str.split(' ').join('');
    7    
    8    // Method 3: Using filter
    9    // return [...str].filter(char => char !== ' ').join('');
    10}
    11removeWhitespace("hello  world  js"); // Output: "helloworldjs"

18. 18. Check if a String is a Valid Shuffle of Two Strings
    1function isValidShuffle(str1, str2, result) {
    2    // Check if lengths match
    3    if(str1.length + str2.length !== result.length) return false;
    4    
    5    // Convert strings to arrays and sort them
    6    const sortedResult = [...result].sort().join('');
    7    const sortedExpected = [...str1 + str2].sort().join('');
    8    
    9    return sortedResult === sortedExpected;
    10}
    11isValidShuffle("abc", "def", "abcdef"); // Output: true
    12isValidShuffle("abc", "def", "abdecf"); // Output: true
    13isValidShuffle("abc", "def", "abcxyz"); // Output: false

19. 19. Convert a String to Title Case
    1function toTitleCase(str) {
    2    return str
    3        .toLowerCase()
    4        .split(' ')
    5        .map(word => word.charAt(0).toUpperCase() + word.slice(1))
    6        .join(' ');
    7}
    8toTitleCase("hello world js"); // Output: "Hello World Js"

20. 20. Find the Longest Common Prefix
    1function longestCommonPrefix(strs) {
    2    if(!strs.length) return "";
    3    
    4    let prefix = strs[0];
    5    for(let i = 1; i < strs.length; i++) {
    6        while(strs[i].indexOf(prefix) !== 0) {
    7            prefix = prefix.slice(0, -1);
    8            if(!prefix) return "";
    9        }
    10    }
    11    return prefix;
    12}
    13longestCommonPrefix(["flower", "flow", "flight"]); // Output: "fl"

21. 21. Convert a String to a Character Array
    1function stringToCharArray(str) {
    2    // Method 1: Using spread operator
    3    return [...str];
    4    
    5    // Method 2: Using split
    6    // return str.split('');
    7    
    8    // Method 3: Using Array.from
    9    // return Array.from(str);
    10}
    11stringToCharArray("hello"); // Output: ['h', 'e', 'l', 'l', 'o']

22. 22. Replace Spaces with %20 (URL Encoding)
    1function urlEncode(str) {
    2    // Method 1: Using encodeURIComponent
    3    return encodeURIComponent(str);
    4    
    5    // Method 2: Manual replacement
    6    // return str.replace(/\s/g, '%20');
    7}
    8urlEncode("hello world js"); // Output: "hello%20world%20js"

23. 23. Convert a Sentence into an Acronym
    1function createAcronym(str) {
    2    return str
    3        .split(' ')
    4        .map(word => word.charAt(0).toUpperCase())
    5        .join('');
    6}
    7createAcronym("World Health Organization"); // Output: "WHO"

24. 24. Check if a String Contains Only Digits
    1function containsOnlyDigits(str) {
    2    // Method 1: Using regex
    3    return /^\d+$/.test(str);
    4    
    5    // Method 2: Using every
    6    // return [...str].every(char => char >= '0' && char <= '9');
    7}
    8containsOnlyDigits("12345"); // Output: true
    9containsOnlyDigits("123a45"); // Output: false

25. 25. Find the Number of Words in a String
    1function countWords(str) {
    2    // Method 1: Split and filter
    3    return str.trim().split(/\s+/).filter(Boolean).length;
    4    
    5    // Method 2: Using match
    6    // return (str.trim().match(/\S+/g) || []).length;
    7}
    8countWords("  Hello   world  JS  "); // Output: 3

26. 26. Remove a Given Character from a String
    1function removeCharacter(str, char) {
    2    // Method 1: Using replace
    3    return str.replace(new RegExp(char, 'g'), '');
    4    
    5    // Method 2: Using split and join
    6    // return str.split(char).join('');
    7}
    8removeCharacter("hello world", "l"); // Output: "heo word"

27. 27. Find the Shortest Word in a String
    1function findShortestWord(str) {
    2    return str
    3        .split(' ')
    4        .reduce((shortest, current) => 
    5            current.length < shortest.length ? current : shortest
    6        );
    7}
    8findShortestWord("The quick brown fox"); // Output: "The"

28. 28. Find the Longest Palindromic Substring
    1function longestPalindromicSubstring(str) {
    2    let start = 0;
    3    let maxLength = 1;
    4    
    5    function expandAroundCenter(left, right) {
    6        while(left >= 0 && right < str.length && str[left] === str[right]) {
    7            const currentLength = right - left + 1;
    8            if(currentLength > maxLength) {
    9                start = left;
    10                maxLength = currentLength;
    11            }
    12            left--;
    13            right++;
    14        }
    15    }
    16    
    17    for(let i = 0; i < str.length; i++) {
    18        expandAroundCenter(i, i);     // Odd length palindromes
    19        expandAroundCenter(i, i + 1); // Even length palindromes
    20    }
    21    
    22    return str.substring(start, start + maxLength);
    23}
    24longestPalindromicSubstring("babad"); // Output: "bab" or "aba"
    25longestPalindromicSubstring("cbbd"); // Output: "bb"

29. 29. Count Vowels in String
    1function countVowels(str) {
    2    // Convert string to lowercase for easier checking
    3    str = str.toLowerCase();
    4    let count = 0;
    5    const vowels = ['a', 'e', 'i', 'o', 'u'];
    6    
    7    // Method 1: Using loop
    8    for(let char of str) {
    9        if(vowels.includes(char)) {
    10            count++;
    11        }
    12    }
    13    return count;
    14    
    15    // Method 2: Using regex
    16    // return str.match(/[aeiou]/gi)?.length || 0;
    17}
    18countVowels("JavaScript"); // Output: 3
    19

30. 30. Find Maximum Number in Array
    1function findMax(arr) {
    2    // Method 1: Using Math.max()
    3    return Math.max(...arr);
    4    
    5    // Method 2: Using loop
    6    // let max = arr[0];
    7    // for(let i = 1; i < arr.length; i++) {
    8    //     if(arr[i] > max) {
    9    //         max = arr[i];
    10    //     }
    11    // }
    12    // return max;
    13}
    14findMax([5, 12, 3, 8, 9]); // Output: 12
    15

31. 31. Check if Number is Prime
    1function isPrime(num) {
    2    // Handle edge cases
    3    if(num <= 1) return false;
    4    if(num <= 3) return true;
    5    
    6    // Check for divisibility up to square root
    7    for(let i = 2; i <= Math.sqrt(num); i++) {
    8        if(num % i === 0) {
    9            return false;
    10        }
    11    }
    12    return true;
    13}
    14isPrime(17); // Output: true
    15isPrime(4);  // Output: false
    16

32. 32. Remove Duplicates from Array
    1function removeDuplicates(arr) {
    2    // Method 1: Using Set
    3    return [...new Set(arr)];
    4    
    5    // Method 2: Using filter
    6    // return arr.filter((item, index) => arr.indexOf(item) === index);
    7    
    8    // Method 3: Using reduce
    9    // return arr.reduce((unique, item) => 
    10    //     unique.includes(item) ? unique : [...unique, item], 
    11    // []);
    12}
    13removeDuplicates([1, 2, 2, 3, 3, 4, 5, 5]); // Output: [1, 2, 3, 4, 5]
    14

33. 33. Capitalize First Letter of Each Word
    1function capitalizeWords(str) {
    2    // Method 1: Using map
    3    return str
    4        .split(' ')
    5        .map(word => word.charAt(0).toUpperCase() + word.slice(1))
    6        .join(' ');
    7    
    8    // Method 2: Using replace
    9    // return str.replace(/\b\w/g, char => char.toUpperCase());
    10}
    11capitalizeWords("hello world"); // Output: "Hello World"
    12

34. 34. Sum of Array Elements
    1function arraySum(arr) {
    2    // Method 1: Using reduce
    3    return arr.reduce((sum, num) => sum + num, 0);
    4    
    5    // Method 2: Using forEach
    6    // let sum = 0;
    7    // arr.forEach(num => sum += num);
    8    // return sum;
    9    
    10    // Method 3: Using for...of
    11    // let sum = 0;
    12    // for(let num of arr) {
    13    //     sum += num;
    14    // }
    15    // return sum;
    16}
    17arraySum([1, 2, 3, 4, 5]); // Output: 15
    18