project_euler_6.rb

# Sum square difference
# Problem 6
#
# The sum of the squares of the first ten natural numbers is,
# 1^2 + 2^2 + ... + 10^2 = 385
# The square of the sum of the first ten natural numbers is,
# (1 + 2 + ... + 10)^2 = 55^2 = 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.

sum_of_squares = 1.upto(100).map { |n| n**2 }.reduce(:+)
square_of_sum = 1.upto(100).reduce(:+)**2

puts square_of_sum - sum_of_squares