JavaScript Questions

1. Palindrome Checker

Given an integer x, return true if x is a palindrome, and false otherwise.

• Example 1:

Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left.

• Example 2:

Input: x = -121 Output: false Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

• Example 3:

Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Function Definition

/**
 * Function to check if a number is a palindrome.
 * @param {number} x - The integer to check.
 * @returns {boolean} - Returns true if the integer is a palindrome, otherwise false.
 */
const isPalindrome = function (x) {
  return x === +x.toString().split("").reverse().join("");
};

// Example Usage
const res = isPalindrome(10);
console.log(res); // Output: false

2. Fibonacci Number

Difficulty: Easy

Problem Description

The Fibonacci numbers, commonly denoted F(n), form a sequence called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

• F(0) = 0, F(1) = 1
• F(n) = F(n - 1) + F(n - 2), for n > 1.

Given n, calculate F(n).

Example 1

Input : n = 2 Output : 1 Explanation : F(2) = F(1) + F(0) = 1 + 0 = 1.

Example 2

Input : n = 3 Output : 2 Explanation : F(3) = F(2) + F(1) = 1 + 1 = 2.

Example 3

Input : n = 4 Output : 3 Explanation : F(4) = F(3) + F(2) = 2 + 1 = 3.

Function Definition

const fib = function (n) {
  if (n <= 1) return n;

  return fib(n - 1) + fib(n - 2);
};

Explanation

1. Base Case :

• The function starts by checking if n is less than or equal to 1.
• If n is 0 , the function return 0
• If n is 1, the function return 1
• These are the base cases for the Fibonacci sequence and represent the first two numbers in the sequence.

2. Recursive Case :

• If n is greater than 1, the function calls itself twice, once with `

3. Missing Number

This algorithm is designed to find the missing number in an array of integers where the numbers range from 0 to n, but one number is missing.

Code:

/**
 * @param {number[]} nums
 * @return {number}
 */
const missingNumber = function (nums) {
  const expectedSum = (nums.length * (nums.length + 1)) / 2;
  return expectedSum - nums.reduce((acc, num) => acc + num, 0);
};

Step-by-Step Explanation :

• Step 1: Calculating Expected Sum

const expectedSum = (nums.length * (nums.length + 1)) / 2;

• Step 2: Calculating Actual Sum

nums.reduce((acc, num) => acc + num, 0);

• The reduce function is used to sum all the numbers present in the array.

• For example, if the array is [0, 1, 3, 4], the sum will be : 0+1+3+4=8

• Step 3: Finding the Missing Number

return expectedSum - nums.reduce((acc, num) => acc + num, 0);

• The missing number is calculated by subtracting the actual sum from the expected sum.
• In the example above, if the expected sum is15and the actual sum is 8, then the missing number is: 15−8=7

Summary :

• Expected Sum: We calculate the expected sum for numbers from 0 to n using the formula n \* (n + 1) / 2.
• Actual Sum: Using the reduce function, we calculate the sum of the numbers present in the array.
• Missing Number: The difference between the expected sum and the actual sum gives the missing number.

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4. Capitalize Sentence

Problem:

Given a sentence, capitalize the first letter of each word.

Solution:

function capitalizeSentence(sentence) {
    return sentence
        .split(' ')
        .map(word => word.charAt(0).toUpperCase() + word.slice(1).toLowerCase())
        .join(' ');
}

Example:

console.log(capitalizeSentence("hello world! this is javascript."));
// Output: "Hello World! This Is Javascript."

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5. FizzBuzz

Problem:

Print numbers from 1 to n. For multiples of 3, print “Fizz” instead of the number. For multiples of 5, print “Buzz”. For numbers divisible by both 3 and 5, print “FizzBuzz”.

Solution:

function fizzBuzz(n) {
    for (let i = 1; i <= n; i++) {
        if (i % 3 === 0 && i % 5 === 0) {
            console.log("FizzBuzz");
        } else if (i % 3 === 0) {
            console.log("Fizz");
        } else if (i % 5 === 0) {
            console.log("Buzz");
        } else {
            console.log(i);
        }
    }
}

Example:

fizzBuzz(20);

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6. Maximum Profit (Stock Trading)

Problem:

Given an array of stock prices, find the maximum profit you can achieve by buying and selling once.

Solution:

function maxProfit(prices) {
    let minPrice = Infinity, maxProfit = 0;
    for (let price of prices) {
        minPrice = Math.min(minPrice, price);
        maxProfit = Math.max(maxProfit, price - minPrice);
    }
    return maxProfit;
}

Example:

console.log(maxProfit([7, 1, 5, 3, 6, 4]));  // Output: 5 (Buy at 1, Sell at 6)
console.log(maxProfit([7, 6, 4, 3, 1]));  // Output: 0 (No profit possible)

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7. Find Student in Array

This algorithm is designed to search for a student’s name in an array of student names. If the name is found, it will print the student’s name.

Problem Description

Given an array of student names and a target name to search for, check if the name exists in the array. If found, print the name; otherwise, do nothing.

Example 1

Input :

const studentDB = ["Saurabh", "Banti", "Raju", "Rajesh", "Dipali"];

findStudent(studentData, "Saurabh");

Output :

Saurabh

Explanation : The name “Saurabh” is found in the array, so it is printed.

Example 2

Input :

findStudent(studentData, "Amit");

Output :

(No Output)

Explanation : The name “Amit” is not found, so nothing is printed.

Function Definition

/**
 * Function to find and print a student's name from an array.
 * @param {string[]} allStudents - Array of student names.
 * @param {string} studentName - The name to search for.
 */

const findStudentName = (data, name) => {
  for (let i = 0; i < data.length; i++) {
    if (data[i] === name) {
      return data[i];
    }
  }
  return false;
};

// console.log(findStudentName(studentDB, "Raju"));

### Step-by-Step Explanation:

1. Input Parameters:

* allStudents: An array containing the names of all students.
* studentName: The name of the student to find.


2. For Loop:

```js
 for (let i = 0; i < data.length; i++) {
    if (data[i] === name) {
      return data[i];
    }
  }

• The loop starts at index 0 and continues until the end of the array.
• i is used as the index to access each student’s name.

3. Condition Check:

  if (data[i] === name) {
      return data[i];
    }

• Checks if the current name in the array is equal to the studentName.
• If a match is found, it prints the name using console.log.

4. Output:

• If the name is found, it prints the student’s name.
• If the name is not found, nothing is printed.

Example Usage:

const studentDB = ["Saurabh", "Banti", "Raju", "Rajesh", "Dipali"];

findStudent(studentData, "Saurabh"); // Output: Saurabh
findStudent(studentData, "Amit");   // No Output

Summary:

• The function iterates through the array using a for loop.
• It checks each name to see if it matches the given studentName.
• If a match is found, it prints the name.
• If no match is found, the loop ends without any output.