Snippet

project_euler/4.rb

Code:

# Project Euler Problem 4: Largest Palindrome Product

# https://projecteuler.net/problem=4

# A palindromic number reads the same both ways.
# 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.

def palindrome?(n)
    n.to_s == n.to_s.reverse
end

def solve(digits)
    solutions = []
    (10 ** digits).times do |n|
        (10 ** digits).times do |m|
            solutions << n * m if palindrome?(n * m)
        end
    end
    return solutions.max
end

puts solve(2)
puts solve(3)

Output:

9009
906609