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Project Euler 38

Project Euler

Problem38を解きました.

  • Pandigital multiples

Take the number 192 and multiply it by each of 1, 2, and 3:

192 × 1 = 192
192 × 2 = 384
192 × 3 = 576
By concatenating each product we get the 1 to 9 pandigital, 192384576. We will call 192384576 the concatenated product of 192 and (1,2,3)

The same can be achieved by starting with 9 and multiplying by 1, 2, 3, 4, and 5, giving the pandigital, 918273645, which is the concatenated product of 9 and (1,2,3,4,5).

What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1,2, ... , n) where n > 1?

https://projecteuler.net/problem=38

問題は「自然数と(1,2,...,n) との連結積として得られる9桁のパンデジタル数の最大値を求めよ.ただしnは2以上の自然数」.

max = 0
for i in 1..9999 do
  k = 2
  str = i.to_s
  while str.length < 9
    str += (i * k).to_s
    k += 1
  end
  compStr = str.split('').sort.join
  max = str.to_i if compStr == '123456789' && max < str.to_i
end

p max

条件から5桁以上の自然数では無いことがわかります.