From One End To The Other (Lua)

from_one_end_to_the_other.lua

-- Week 4: From One End to the Other: Find the smallest possible (positive)
-- integer that ends in a six such that if that six is removed and placed in front
-- of the remaining digits of the number, the resulting number will be four times
-- as large as the original.

function swap_first_and_last(t, n)
  table.insert(t, 1, n)
  return tonumber(table.concat(t))
end

for i = 6, 1000000, 2 do
  local digits = {}
  local count = 1

  for x in string.gmatch(tostring(i), "%S") do
    table.insert(digits, count, x)
    count = count + 1
  end

  local last = table.remove(digits)

  if last == "6" and swap_first_and_last(digits, last) == i * 4 then
    print(i)
    os.exit()
  end
end

-- $ lua from_one_end_to_the_other.lua
-- 153846