🔄 Array & String Logic

• 1. Remove Duplicates from Array

  Use Set to eliminate duplicate values as it stores only unique entries.

  const arr = [1, 2, 2, 3, 4, 4, 5];
  const unique = [...new Set(arr)];
  console.log(unique); // [1, 2, 3, 4, 5]

  Use filter() and indexOf() to keep the first occurrence of each item.

  const arr = [1, 2, 2, 3, 4, 4, 5];
  const unique = arr.filter((value, index, self) => self.indexOf(value) === index);
  console.log(unique); // [1, 2, 3, 4, 5]

  Use reduce() to build a unique array manually.

  const arr = [1, 2, 2, 3, 4, 4, 5];
  const unique = arr.reduce((acc, curr) => {
    if (!acc.includes(curr)) acc.push(curr);
    return acc;
  }, []);
  console.log(unique); // [1, 2, 3, 4, 5]

  Use a for loop and check if value already exists in the result array.

  const arr = [1, 2, 2, 3, 4, 4, 5];
  const unique = [];
  for (let i = 0; i < arr.length; i++) {
    if (!unique.includes(arr[i])) unique.push(arr[i]);
  }
  console.log(unique); // [1, 2, 3, 4, 5]

• 2. Reverse a String

  Use split, reverse, and join to reverse characters.

  const str = "hello";
  const reversed = str.split('').reverse().join('');
  console.log(reversed); // "olleh"

  Use a for loop to reverse manually.

  const str = "hello";
  let reversed = "";
  for (let i = str.length - 1; i >= 0; i--) {
    reversed += str[i];
  }
  console.log(reversed); // "olleh"

  Use reduce() for a functional approach to reverse.

  const str = "hello";
  const reversed = str.split('').reduce((rev, char) => char + rev, '');
  console.log(reversed); // "olleh"

• 3. Check Palindrome

  Check if a string reads the same forward and backward.

  function isPalindrome(s) {
    return s === s.split('').reverse().join('');
  }
  console.log(isPalindrome("racecar")); // true

• 4. Find Maximum and Minimum in Array

  Use Math.max() and Math.min() with spread syntax.

  const arr = [1, 3, 2, 5];
  console.log(Math.max(...arr)); // 5
  console.log(Math.min(...arr)); // 1

• 5. Flatten Nested Array

  Use flat(Infinity) to recursively flatten all nested arrays.

  const arr = [1, [2, [3, [4]]]];
  console.log(arr.flat(Infinity)); // [1, 2, 3, 4]

• 6. Check Anagram

  Anagrams are strings with same characters in different order.

  const isAnagram = (a, b) =>
    a.split('').sort().join('') === b.split('').sort().join('');
  console.log(isAnagram("listen", "silent")); // true

• 7. Find Missing Number in Sequence

  Use the formula sum of 1 to n to find the missing number.

  const missing = (arr) => {
    let n = arr.length + 1;
    let expected = (n * (n + 1)) / 2;
    let actual = arr.reduce((a, b) => a + b, 0);
    return expected - actual;
  };
  console.log(missing([1, 2, 4, 5])); // 3

• 8. Count Occurrence of Each Character

  Loop through each character and count how many times it appears.

  const str = "hello";
  const count = {};
  for (let char of str) {
    count[char] = (count[char] || 0) + 1;
  }
  console.log(count); // { h: 1, e: 1, l: 2, o: 1 }

• 9. Find First Non-Repeating Character

  Find the first character whose first and last index are same.

  const str = "swiss";
  const result = str.split('').find(c => str.indexOf(c) === str.lastIndexOf(c));
  console.log(result); // "w"

• 10. Sum of All Elements

  Use reduce() to accumulate the sum of array elements.

  const arr = [1, 2, 3, 4];
  const sum = arr.reduce((a, b) => a + b, 0);
  console.log(sum); // 10