Back to basics : Top interview logical programs in javascript

• The most asked logical programs in the interview

During the technical interview, these types of logical programs may ask you. These questions are common in any software programmer role.
I have picked a bunch of logical programming interview question that are using javascript and it may help you to crack your interview.
The following programs to be narrated.

Table of contents

• 1. Fibonacci

• 2. Prime Numbers

• 3. Pyramid star pattern

• 4. Amstrong numbers

• 1. Fibonacci series using recursive function in javascript

In this program snippet you going to learn how to write the Fibonacci series. To understand the logic you should need javascript knowledge. Also we going to learn or familiar the recursive function.
A recursive function is a function in code that refers to itself for execution. Recursive functions can be simple or elaborate.
What is fibonacci?
A series of numbers in which each number ( Fibonacci number ) is the sum of the two preceding numbers. The simplest is the series 1, 1, 2, 3, 5, 8, etc.

Let's go to the program and will examine how it works!

// program to display fibonacci sequence using recursion
function fibonacci(num) {
    if(num < 2) {
        return num;
    }
    else {
        return fibonacci(num-1) + fibonacci(num - 2);
    }
}

// set the nth term
let nThTerms = 5;
if(nThTerms <=0) {
    console.log('Enter a positive integer.');
}
else {
    for(let i = 0; i < nThTerms; i++) {
        console.log(fibonacci(i));
    }
}

Result

Enter the number of terms: 5
0
1
1
2
3

Hope the program is helped to understand the logic, we go to next coding example.

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• 2. Find the prime numbers in javascirpt

let's do the coding for finding out the prime number.
What is prime number
A prime number is a number that is divisible by 1 and itself only. E.g.:- prime numbers are: 2, 3, 5, 7, 11, 13, 17...
Basically, when you doing division to any number, if the remainder is 0 then it is a prime number otherwise it is not.

const primeNumber=number % i == 0

function isPrimeNumber(num) {
  let isPrime = true;
  if (num == 1) {
    return true;
  } else {
    for (let i = 2; i < num; i++) {
      if (num % i === 0) {
        isPrime = false;
        break;
      }
    }
    if (isPrime) {
      console.log(isPrime + " is a prime number");
    } else {
      console.log(isPrime + " is not a prime number");
    }
  }
}
isPrimeNumber(10)
isPrimeNumber(11)

Result

10 is a prime number
11 is a prime number

if you want to check the series of prime number then use for loop and use the isPrimeNumber function and pass the number.

 for (let i = 2; i < 10; i++) 
   {
     isPrimeNumber(i)
   }

Result

"2 is a prime number"
"3 is a prime number"
"4 is not a prime number"
"5 is a prime number"
"6 is not a prime number"
"7 is a prime number"
"8 is not a prime number"
"9 is not a prime number"

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• 3. Pyramid star pattern in javascript**

The pyramid pattern is very popular star pattern, you can see the example below

    *
   ***
  *****
 *******
*********

To achieve this pattern use the below code in your program.

let n = 5;
let string = "";

for (let i = 1; i <= n; i++) {
  
  for (let j = 1; j <= n - i; j++) {
    string += " ";
  }
  
  for (let k = 0; k < 2 * i - 1; k++) {
    string += "*";
  }
  string += "\n";
}
console.log(string);

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• 4. Check amstrong number using javascript

In this program, you will learn to write a program for finding out the given number is amstrong or not.
What is amstrong number
if the sum of its own digits raised to the power number of digits gives the number itself.

function amstrong(num) {
  let num1 = num;
  let sum = 0;
  while (num > 0) {
    rem = num % 10;
    sum = sum + Math.pow(rem, num1.toString().length);
    num = parseInt(num / 10);
  }
  if (sum == num1) {
    console.log(num+" is Armstrong");
  } else {
    console.log(num+" is not Armstrong");
  }
}
amstrong(153);
amstrong(154);

Result

'153 is Armstrong'
'154 is not Armstrong'

You might have doubt how 153 is Armstrong and why 154 is not.

153 = (111)+(555)+(333)
where:
(111)=1
(555)=125
(333)=27
So:
1+125+27=153

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