Switching to Ruby for a quick one-liner of Project Euler.
Problem 20:
Factorial Digit Sum
n! means n × (n − 1) × … × 3 × 2 × 1
For example, 10! = 10 × 9 × … × 3 × 2 × 1 = 3628800,
and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.Find the sum of the digits in the number 100!
I was able to reuse most the code from my Problem 16 solution, I just needed to calculate the factorial at the beginning of it (no built-in factorial function in Ruby).
answer = (1..100).inject(:*).to_s.split('').map(&:to_i).reduce(:+)
puts answer
--output: 648
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