DSA Exercise-1( Time and space complexity)

//Practice Time and space complexity of these examples

//Exercise 1: Sum of All Elements
const sumArray = (arr) => {
  let sum = 0;
  for (let i = 0; i < arr.length; i++) {
    sum += arr[i];
  }
  return sum;
}

console.log(sumArray([1, 2, 3, 4, 5])); // Output: 15

//Exercise 2: Find the Maximum Element
const findMax = (arr) => {
  let max = arr[0];
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] > max) {
      max = arr[i];
    }
  }
  return max;
}

console.log(findMax([1, 2, 3, 4, 5])); // Output: 5


 //Exercise 3: Reverse an Array
const reverseArray = (arr) => {
  let left = 0;
  let right = arr.length - 1;
  while (left < right) {
    [arr[left], arr[right]] = [arr[right], arr[left]]; // Swap elements
    left++;
    right--;
  }
  return arr;
}

console.log(reverseArray([1, 2, 3, 4, 5])); // Output: [5, 4, 3, 2, 1]


//4. Exercise 4: Check if a String is a Palindrom
//Write a function to check if a given string is a palindrome (reads the same forward and backward).
const isPalindrome = (str) => {
  let left = 0;
  let right = str.length - 1;

  while (left < right) {
    if (str[left] !== str[right]) {
      return false;
    }
    left++;
    right--;
  }

  return true;
}

console.log(isPalindrome("racecar")); // Output: true
console.log(isPalindrome("hello"));   // Output: false


//5. Exercise 5: Count Distinct Elements

const countDistinct = (arr) => {
  const uniqueElements = new Set(arr);
  return uniqueElements.size;
}

console.log(countDistinct([1, 2, 2, 3, 4, 4, 5])); // Output: 5

//6. Exercise 6: Two Sum Problem
Write a function that returns the indices of two numbers in an array that add up to a given target.
const twoSum = (arr, target) => {
  const map = new Map();

  for (let i = 0; i < arr.length; i++) {
    const complement = target - arr[i];
    if (map.has(complement)) {
      return [map.get(complement), i];
    }
    map.set(arr[i], i);
  }

  return [];
}


// 7. Exercise 7: Merge Two Sorted Arrays
const mergeSortedArrays = (arr1, arr2) => {
  let i = 0, j = 0;
  const merged = [];

  while (i < arr1.length && j < arr2.length) {
    if (arr1[i] < arr2[j]) {
      merged.push(arr1[i]);
      i++;
    } else {
      merged.push(arr2[j]);
      j++;
    }
  }

  while (i < arr1.length) {
    merged.push(arr1[i]);
    i++;
  }

  while (j < arr2.length) {
    merged.push(arr2[j]);
    j++;
  }

  return merged;
}

console.log(mergeSortedArrays([1, 3, 5], [2, 4, 6])); // Output: [1, 2, 3, 4, 5, 6]

//8. Exercise 8: Find All Pairs with a Given Sum
Write a function that returns all unique pairs of numbers from an array that add up to a given target sum.

javascript
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const findPairs = (arr, target) => {
  const pairs = [];
  const seen = new Set();

  for (let num of arr) {
    const complement = target - num;
    if (seen.has(complement)) {
      pairs.push([complement, num]);
    }
    seen.add(num);
  }

  return pairs;
}

console.log(findPairs([2, 4, 3, 5, 6, -1, 2, 5], 7)); // Output: [[3, 4], [5, 2], [6, 1]]

//9. Exercise 9: Move Zeroes
//Write a function that moves all the zeroes in an array to the end while maintaining the relative order of the non-zero elements.

const moveZeroes = (arr) => {
  let nonZeroIndex = 0;

  for (let i = 0; i < arr.length; i++) {
    if (arr[i] !== 0) {
      arr[nonZeroIndex++] = arr[i];
    }
  }

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

  return arr;
}

console.log(moveZeroes([0, 1, 0, 3, 12])); // Output: [1, 3, 12, 0, 0]

//10. Exercise 10: First Unique Character in a String
//Write a function that returns the index of the first non-repeating character in a string. If all characters are repeated, return -1.


const firstUniqueChar = (str) => {
  const charCount = {};

  for (let char of str) {
    charCount[char] = (charCount[char] || 0) + 1;
  }

  for (let i = 0; i < str.length; i++) {
    if (charCount[str[i]] === 1) {
      return i;
    }
  }

  return -1;
}

console.log(firstUniqueChar("leetcode")); // Output: 0
console.log(firstUniqueChar("loveleetcode")); // Output: 2
console.log(firstUniqueChar("aabb")); // Output: -1