Solving the challenge

"The most dangerous phrase in the language is, 'We've always done it this way.'" - Grace Hopper

This is a series of posts that will focus on solving the daily problems posed by the user @ydavgonzalez step by step and we will also teach the programming approach.

challenge link

Let's dive into the fascinating world of divisors and unlock the secrets behind counting them! Our mission is to find out how many two-digit divisors the number 102400 possesses. This problem may seem daunting at first, but fear not! We'll break it down into digestible steps, unveiling the elegance of prime factorization along the way.

Understanding Divisors:

A divisor of a number divides that number evenly, leaving no remainder. For instance, 4 is a divisor of 12 because 12 / 4 = 3.

Prime Factorization: The Key:

The foundation of our quest lies in prime factorization. Every number greater than 1 can be expressed as a unique product of prime numbers. Prime numbers are like the building blocks of numbers, and their powers reveal the structure of a number's divisors.

Let's prime factorize 102400:

102400 = 2^10 * 5^3

Counting Divisors:

Now, we'll use the prime factors to count the divisors. Here's the rule:

• For each prime factor, increase its exponent by 1.
• Multiply these increased exponents together.

In our case:

• Exponents of 2 and 5 increase to 11 and 4 respectively.
• Total number of divisors = (11 + 1) * (4 + 1) = 60

This means 102400 has 60 divisors in total. But remember, we're looking for two-digit divisors.

Filtering for Two-Digit Divisors:

Now, we need to narrow down the count to only those divisors between 10 and 99. We can do this systematically by considering the possible combinations of prime factors:

1. Smallest Two-Digit Divisor: The smallest two-digit divisor is 10, which is 2 * 5.
2. Largest Two-Digit Divisor: The largest two-digit divisor is 96, which is 2^5 * 3.
3. Exploring Combinations: We need to find combinations of 2 and 5, along with possible inclusion of 3, that fall within the two-digit range.

JavaScript Code for Counting Two-Digit Divisors:

function countTwoDigitDivisors(number) 
{
  let divisors = 0;
  const primeFactors = factorize(number);

 // Assuming factorize function is implemented 

  for (let i = 1; i <= primeFactors[2]; i++) {
 // 3 is the index for factor 5
    for (let j = 0; j <= primeFactors[0]; j++) {
 // 0 is the index for factor 2
      let divisor = Math.pow(2, j) * Math.pow(5, i);

      Check if divisor is within the two-digit range
      if (divisor >= 10 && divisor <= 99) {
        divisors++;
      }
    }
  }

  return divisors;
}

function factorize(number) {
  let primeFactors = [];
  let factor = 2;

  while (number > 1) {
    if (number % factor === 0) {
      if (!primeFactors[factor]) {
        primeFactors[factor] = 0;
      }
      primeFactors[factor]++;
      number /= factor;
    } else {
      factor++;
    }
  }
  return primeFactors;
}

const number = 102400;
const twoDigitDivisors = countTwoDigitDivisors(number);
console.log(The number of two-digit divisors of ${number} is: ${twoDigitDivisors});

Let's see your solutions! Share your own code in the comments below, whether you use JavaScript, Python, or any other language. Let's explore different approaches to this exciting problem and delve deeper into the world of divisors and prime factorization!