Solving Project Euler Problem 10: Summation of Primes

 Problem

"The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17. Find the sum of all the primes below two million."

Solution

A prime number is a positive integer greater than 1 that has no positive integer divisors other than 1 and itself. In other words, a prime number is a number that cannot be evenly divided by any other number except 1 and itself. For example, the first few prime numbers are 2, 3, 5, 7, 11, and so on. These numbers cannot be divided by any other integer except 1 and themselves, making them prime.

 

1. We define the primess  function, which takes one argument, n, representing the upper limit for prime generation.
2. We initialize a boolean list, is_prime, of length n + 1, where each element initially represents whether a number is prime (True) or not (False). We mark 0 and 1 as non-prime.
3. Using a loop that iterates from 2 to the square root of limit, we iterate through each number and check if it is marked as prime in the is_prime list. If it is, we mark its multiples as non-prime.
4. After the loop finishes, the is_prime list contains True values at indices corresponding to prime numbers.
5. We create a list, prime_numbers, that stores the prime numbers found by enumerating the indices of is_prime where the value is True.
6. Finally, we calculate the sum of all prime numbers below two million using the sum function.

 

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking. 

Solving Project Euler Problem 9: Special Pythagorean Triplet

 Problem

"A Pythagorean triplet is a set of three natural numbers, a < b < c, for which: a² + b² = c²

For example, 3² + 4² = 5² or 9 + 16 = 25. There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product abc."

Solution

A Pythagorean triplet is a set of three positive integers (a, b, c) that satisfy the Pythagorean Theorem: a² + b² = c². In other words, the square of the length of the hypotenuse (the side opposite the right angle) in a right-angled triangle is equal to the sum of the squares of the other two sides. For example, the triplet (3, 4, 5) is a Pythagorean triplet because 3² + 4² = 5². 

 

1.      The special_pythagorean function takes one argument, n, which is the desired sum of a + b + c.

2.      We use a nested loop structure to iterate through all possible values of a and b within the specified range.

3.      Inside the nested loops, we calculate the value of c by subtracting a and b from n (1000).

4.      We check if the current values of a, b, and c form a Pythagorean triplet by verifying if

           a² + b² = c².

5.      If a Pythagorean triplet is found, we break out of the loops and return the values of a, b, and c.

6.      Finally, we calculate the product abc and print the result.

 

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking.

Solving Project Euler Problem 8: Largest Product in a Series

Problem

"The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

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Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?"

Solution

A consecutive digit product is the result of multiplying a sequence of consecutive digits within a larger number. For example, in the 1000-digit number provided in the problem statement, the product of the four consecutive digits "9, 9, 8, 9" is 5832.

To find the largest product of consecutive digits, we need to slide a window of a specified size (in this case, thirteen) through the number and calculate the product of the digits within that window. We then compare the products obtained as we slide the window and keep track of the largest product encountered.

 

1.      We define a helper function, calculate_product, which takes a string of digits and calculates the product of those digits.

2.      The find_largest_product function takes two arguments: number, the large number as a string, and consecutive_digits, the number of consecutive digits to consider.

3.      We initialize max_product to 0, which will store the maximum product encountered.

4.      Using a for loop that iterates through the string representation of the number, we extract a window of consecutive digits of length consecutive_digits.

5.      We calculate the product of the digits within the window using the calculate_product function.

6.      We compare the calculated product with the current max_product and update max_product if the new product is greater.

7.      We continue sliding the window through the string until we reach the end.

8.      After the loop finishes, max_product will contain the largest product of consecutive_digits consecutive digits.

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking.

Solving Project Euler Problem 7: The 10001st Prime Number

 Problem

By listing the first six prime numbers: 2, 3, 5, 7, 11 and 13, we can see that the 6^th prime is 13.  What is the 10 001^st prime number?

 Solution

A prime number is a positive integer greater than 1 that has no positive integer divisors other than 1 and itself. In other words, a prime number is a number that cannot be evenly divided by any other number except 1 and itself.

For example, the first few prime numbers are 2, 3, 5, 7, 11, and 13. These numbers cannot be divided by any other integer except 1 and themselves, making them prime.

 

 

1.      We define a helper function, prime, which takes an integer n as input and checks if it is prime. The function first handles special cases (1 and 2) and then uses a common optimization for prime checking, which involves checking divisibility only up to the square root of n.

2.      The find_10001st_prime function is responsible for finding the 10,001st prime number. It initializes count to 0 and number to 2.

3.      The while loop continues indefinitely until we find the 10,001st prime number.

4.      Inside the loop, we use the prime function to check if number is prime. If it is, we increment the count by 1.

5.      If count reaches 10,001, we break out of the loop because we have found the desired prime number.

6.      Otherwise, if number is not prime, we increment it by 1 and continue the loop to check the next number.

7.      After the loop finishes, the value of number will be the 10,001st prime number.

 

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking.

 

Solving Project Euler Problem 6: Sum Square Difference

 Problem

"The sum of the squares of the first ten natural numbers is: 1² + 2² + ... + 10² = 385

The square of the sum of the first ten natural numbers is: (1 + 2 + ... + 10)² = 55² = 3025

Hence, the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 - 385 = 2640. Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum."

 

Solution

1.      Sum of the Squares: To find the sum of the squares of the first n natural numbers, we calculate the square of each number from 1 to n and then add those squares together. Mathematically, this can be expressed as:

Sum of Squares = 1² + 2² + 3² + ... + n²

2.      Square of the Sum: To find the square of the sum of the first n natural numbers, we first calculate the sum of those numbers and then square the result. Mathematically, this can be expressed as:

Square of Sum = (1 + 2 + 3 + ... + n)²

 

The problem asks for the difference between these two quantities, which can be calculated as:

Difference = Square of Sum – Sum of Squares

 

1.      We define a function, sum_square_difference, that takes one argument, n, representing the number of natural numbers we want to consider (in this case, 100).

2.      We initialize sum_of_squares and square_of_sum to zero as our starting points.

3.      Using a for loop that iterates from 1 to n (inclusive), we calculate the sum of the squares of the first n natural numbers and the sum of the first n natural numbers.

4.      After the loop finishes, we calculate the square of the sum by squaring the value of square_of_sum.

5.      Finally, we calculate the difference between the square of the sum and the sum of the squares, which is the result we are looking for.

 

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking.

 

 

 

Solving Project Euler Problem 5: Smallest Multiple

 Problem

"2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder. What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?"

Solution

To solve this problem, we need to understand the concept of the smallest multiple. A multiple of a number is a result of multiplying that number by any integer. For example, the multiples of 3 are 3, 6, 9, 12, 15, 18, and so on.

The smallest multiple that is divisible by a set of numbers is called the least common multiple (LCM) of those numbers. To find the LCM of two numbers, we can use the greatest common divisor (GCD) of those numbers. The relationship between LCM and GCD is given by the formula:

LCM(a, b) = (a * b) / GCD(a, b)

This formula can be extended to find the LCM of more than two numbers by iteratively calculating the LCM of pairs of numbers.

 

1.      We define a helper function, gcd, which calculates the greatest common divisor (GCD) of two numbers using the Euclidean algorithm.

2.      Another helper function, lcm, calculates the least common multiple (LCM) of two numbers using the LCM formula we discussed earlier.

3.      The smallest_multiple function takes one argument, n, which represents the upper limit (in this case, 20) for the range of numbers for which we want to find the smallest multiple.

4.      We initialize result to 1 as the starting point.

5.      Using a loop that iterates through all numbers from 1 to n, we update result by finding the LCM of result and the current number.

6.      After the loop finishes, result will contain the smallest positive number that is evenly divisible by all numbers from 1 to n.

 

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking.

 

 

 

 

 

 

Solving Project Euler Problem 4: Largest Palindrome Product

 Problem

A palindromic number reads the same forwards and backwards. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99. Find the largest palindrome made from the product of two 3-digit numbers."

Solution

A palindrome is a sequence of characters (or in this case, digits) that reads the same forwards and backwards. Examples of palindromes include "racecar," "level," and "deified." In the context of this problem, we are looking for palindromic numbers.

For example, consider the number 9009. It is a palindrome because it reads the same forwards and backwards. When expressed as the product of two 2-digit numbers (91 and 99), it fulfills the conditions set by the problem.

 

1.      We define a helper function, palindrome_number, which takes a number as input, converts it to a string, and checks if it's the same forwards and backwards.

2.      The largest_palindrome function takes one argument, n, which represents the number of digits in the numbers we want to multiply.

3.      We initialize larg_palindrome to zero and initial to the largest n-digit number (e.g., 999 for n=3).

4.      We use nested loops to iterate through all possible combinations of n-digit numbers, starting from the largest values and moving downwards.

5.      Inside the loops, we calculate the product of a and b.

6.      We check if the product is a palindrome using the palindrome_number function and if it's greater than the current larg_palindrome. If both conditions are met, we update larg_palindrome with the new value.

7.      After the loops finish, larg_palindrome contains the largest palindrome product of two n-digit numbers.

 

Solving Project Euler Problems provides a great opportunity to practice coding and algorithmic thinking.