題目看起來好理解，想下及翻閱 API 後，
透過組合技便能完成題目。

Codewars LV6

題目(Write Number in Expanded Form)：

Write Number in Expanded Form
You will be given a number and you will need to return it as a string in Expanded Form. For example:

expanded_form(12); # Should return '10 + 2'
expanded_form(42); # Should return '40 + 2'
expanded_form(70304); # Should return '70000 + 300 + 4'
NOTE: All numbers will be whole numbers greater than 0.

def expanded_form(num)
  # Your code here
end

it "Example cases" do
  Test.assert_equals(expanded_form(12), '10 + 2')
  Test.assert_equals(expanded_form(42), '40 + 2')
  Test.assert_equals(expanded_form(70304), '70000 + 300 + 4')
end

影片解題：

答案：

# Write Number in Expanded Form
def expanded_form(num)
  num.to_s
     .reverse
     .chars
     .map.with_index{| x, i | x == '0' ? nil : x + '0' * i }.compact
     .reverse
     .join' + '
end

本文同步發布於 小菜的 Blog https://riverye.com/