Project Euler with Ruby on WSL [Problem 5]

例によって

ネタばれというか解答ありです

問題文

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?

私訳

1から20までのすべての数で割り切れる、最小の正整数はなにか

つまり、最小公倍数は？

解答方針

で なので、ごく単純に lcm を取っていく

解答

# Project Euler
# problem 5

def gcd(a, b) # greatest common divisor
    if a > b
        return gcd(b, a)
    end

    r = b % a
    if r == 0
        return a
    end

    gcd(r, a)
end

def lcm(a, b) # least common multiplier
    a * b / gcd(a,b)
end

def lcm_list(list)
    list.reduce(1){|result, item| lcm(result, item)}
end

puts lcm_list(1..20)