Interview Preparations

Problem Solving

1.How can you write the words "one Two Three" in the console when given the variable a = oneTwoThree in Node.js?

To write the words "one Two Three" in the console when given the variable a = oneTwoThree in Node.js, you can split the string at the uppercase letters and then join the resulting array with space character as a separator. Here's an example code snippet:

let a = "oneTwoThree";
let words = a.split(/(?=[A-Z])/).join(" ");
console.log(words); // output: "one Two Three"

In this code, the split() method is used to split the string at each uppercase letter using a regular expression /(?=[A-Z])/. The resulting array is then joined with a space character using the join() method. Finally, the resulting string is printed to the console using console.log().

2.How to find the second maximum value from an array in JavaScript? Can you provide a solution with and without using built-in functions?

Sure, here's one solution to find the second maximum value from an array in JavaScript using a custom function:

function findSecondMax(arr) {
  let max = arr[0];
  let secondMax = null;
 
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] > max) {
      secondMax = max;
      max = arr[i];
    } else if (arr[i] !== max && (secondMax === null || arr[i] > secondMax)) {
      secondMax = arr[i];
    }
  }
 
  return secondMax;
}
 
// Example usage:
const arr = [10, 20, 30, 40, 50];
console.log(findSecondMax(arr)); // Output: 40

This solution iterates through the array and keeps track of the current maximum and second maximum values. It returns the second maximum value at the end.

Here's another solution without using built-in functions:

function findSecondMax(arr) {
  let max = arr[0];
 
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] > max) {
      max = arr[i];
    }
  }
 
  let secondMax = null;
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] !== max && (secondMax === null || arr[i] > secondMax)) {
      secondMax = arr[i];
    }
  }
 
  return secondMax;
}
 
// Example usage:
const arr = [10, 20, 30, 40, 50];
console.log(findSecondMax(arr)); // Output: 40

This solution first finds the maximum value by iterating through the array once. Then it iterates through the array again to find the second maximum value, ignoring the maximum value itself.

3.How can you merge three objects in JavaScript? Can you provide a solution with and without using built-in functions?

Yes, we can merge three objects in JavaScript using both built-in and custom functions. Here are the solutions:

Using Built-in Functions:

const obj1 = { a: 1, b: 2 };
const obj2 = { c: 3, d: 4 };
const obj3 = { e: 5, f: 6 };
 
const mergedObject = Object.assign(obj1, obj2, obj3);
console.log(mergedObject);

Output:

{ a: 1, b: 2, c: 3, d: 4, e: 5, f: 6 }

Using Custom Function:

const obj1 = { a: 1, b: 2 };
const obj2 = { c: 3, d: 4 };
const obj3 = { e: 5, f: 6 };
 
function mergeObjects(...objs) {
  const merged = {};
  for (let i = 0; i < objs.length; i++) {
    const keys = Object.keys(objs[i]);
    for (let j = 0; j < keys.length; j++) {
      merged[keys[j]] = objs[i][keys[j]];
    }
  }
  return merged;
}
 
const mergedObject = mergeObjects(obj1, obj2, obj3);
console.log(mergedObject);

Output:

{ a: 1, b: 2, c: 3, d: 4, e: 5, f: 6 }

Both solutions will merge the objects and create a new object with all the properties from the three objects. The built-in solution uses the Object.assign() method, which merges the objects from left to right. The custom solution uses a function that takes any number of objects and iterates over each property to merge them into a new object.

4.How to merge multiple objects into a single object and remove duplicates in JavaScript? Can you provide a solution with and without using built-in functions?

To merge multiple objects into a single object and remove duplicates in JavaScript, you can use a combination of the spread operator, the reduce() method, and the Object.values() method. Here is an example solution:

Using built-in functions:

const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const obj3 = { c: 5, d: 6 };
 
const merged = Object.values(
  [obj1, obj2, obj3].reduce((acc, cur) => ({ ...acc, ...cur }), {})
);
 
const result = [...new Set(merged)];
 
console.log(result); // [1, 2, 3, 4, 5, 6]

Without using built-in functions:

const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const obj3 = { c: 5, d: 6 };
 
const merged = [obj1, obj2, obj3].reduce((acc, cur) => {
  for (const [key, value] of Object.entries(cur)) {
    if (!acc.hasOwnProperty(key)) {
      acc[key] = value;
    }
  }
  return acc;
}, {});
 
const result = Object.values(merged);
 
console.log(result); // [1, 2, 3, 4, 5, 6]

In both solutions, we first create three objects obj1, obj2, and obj3. We then use the reduce() method to merge these objects into a single object using the spread operator. Finally, we use the Object.values() method to get an array of all the values in the merged object, and then we use the Set object to remove duplicates.

5.How would you find the number of occurrences of a character in a string in JavaScript?

To find the number of occurrences of a character in a string in JavaScript, you can use a combination of split() and filter() methods as follows:

const str = "hello world";
const char = "l";
const count = str.split("").filter((c) => c === char).length;
console.log(count); // 3

Here, the split() method is used to split the string into an array of characters, and then filter() is used to create a new array containing only the matching characters. Finally, the length of the filtered array is returned as the count.

Another way to do this is to use a regular expression and the match() method as follows:

const str = "hello world";
const char = "l";
const regex = new RegExp(char, "g");
const count = (str.match(regex) || []).length;
console.log(count); // 3

Here, a regular expression is created with the g flag to match all occurrences of the character. The match() method is then used to find all the matches in the string, and the length of the resulting array is returned as the count. The || [] is used to handle the case when there are no matches, in which case match() returns null, and the length of null is not defined.

6.Can you explain how to print the outermost elements of a 4x4 matrix in a spiral order?

Yes, sure! To print the outermost elements of a 4x4 matrix in a spiral order, you can follow these steps:

Create the 4x4 matrix and initialize its values.
Create four variables to keep track of the boundaries of the matrix: top, bottom, left, and right.
Loop through the elements of the matrix in a spiral order, starting from the top-left corner and moving clockwise. At each iteration, check if the current element is on the outermost layer of the matrix, and print it if it is.
Update the values of top, bottom, left, and right as you move through the matrix, so that the loop only iterates through the remaining elements.

Here is a code example in JavaScript:

const matrix = [
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9, 10, 11, 12],
  [13, 14, 15, 16],
];
 
let top = 0;
let bottom = matrix.length - 1;
let left = 0;
let right = matrix[0].length - 1;
 
while (top <= bottom && left <= right) {
  // Print top row
  for (let i = left; i <= right; i++) {
    console.log(matrix[top][i]);
  }
  top++;
 
  // Print right column
  for (let i = top; i <= bottom; i++) {
    console.log(matrix[i][right]);
  }
  right--;
 
  // Print bottom row
  if (top <= bottom) {
    for (let i = right; i >= left; i--) {
      console.log(matrix[bottom][i]);
    }
    bottom--;
  }
 
  // Print left column
  if (left <= right) {
    for (let i = bottom; i >= top; i--) {
      console.log(matrix[i][left]);
    }
    left++;
  }
}

This code will output the elements of the 4x4 matrix in a spiral order, starting from the outermost layer:

1;
2;
3;
4;
8;
12;
16;
15;
14;
13;
9;
5;
6;
7;
11;
10;

7.Write a program in Javascript to merge two sorted arrays into a sorted form

Sure, here is an example program in JavaScript to merge two sorted arrays into a sorted form:

function mergeSortedArrays(arr1, arr2) {
  let result = [];
  let i = 0;
  let j = 0;
 
  while (i < arr1.length && j < arr2.length) {
    if (arr1[i] < arr2[j]) {
      result.push(arr1[i]);
      i++;
    } else {
      result.push(arr2[j]);
      j++;
    }
  }
 
  while (i < arr1.length) {
    result.push(arr1[i]);
    i++;
  }
 
  while (j < arr2.length) {
    result.push(arr2[j]);
    j++;
  }
 
  return result;
}
 
// Example usage:
const arr1 = [1, 3, 5, 7];
const arr2 = [2, 4, 6, 8];
const mergedArray = mergeSortedArrays(arr1, arr2);
console.log(mergedArray); // [1, 2, 3, 4, 5, 6, 7, 8]

In this program, we define a function mergeSortedArrays that takes in two sorted arrays arr1 and arr2 as input, and returns a new array that contains all the elements of arr1 and arr2 in a sorted form. The function uses a while loop to iterate over both arrays simultaneously, comparing the elements at the current index of each array and adding the smaller element to the result array. Once the loop has finished iterating over one of the arrays, the remaining elements of the other array are added to the result array. Finally, the result array is returned.

8.Write a program in Javascript to shift the kth element of an array from the start to the end.

Here's an example program in JavaScript to shift the kth element of an array from the start to the end:

function shiftKthElement(arr, k) {
  // Calculate the index of the kth element from the start
  const kIndex = k - 1;
  // Remove the kth element from the start and save it to a variable
  const kElement = arr.splice(kIndex, 1)[0];
  // Add the kth element to the end of the array
  arr.push(kElement);
  // Return the updated array
  return arr;
}
 
// Example usage
const arr = [1, 2, 3, 4, 5];
console.log(shiftKthElement(arr, 2)); // Output: [1, 3, 4, 5, 2]

In this program, the shiftKthElement function takes two arguments: an array and the index (k) of the element to be shifted from the start to the end of the array.

First, we calculate the index of the kth element from the start (subtracting 1 since arrays are zero-indexed). Then, we use the splice method to remove the kth element from the start of the array and save it to a variable.

Next, we use the push method to add the kth element to the end of the array. Finally, we return the updated array.

In the example usage, we pass an array [1, 2, 3, 4, 5] and k value of 2 to the shiftKthElement function. The output will be [1, 3, 4, 5, 2], which is the updated array with the second element (2) shifted from the start to the end.

9.How can you count the number of occurrences of a particular character in a JavaScript String,

and what are some different approaches that can be used to achieve this?

What Is Node.js Scenario