I was looking at leetcode and found this problem. I got nostalia'd hard since I actually started out writing VBA for Excel, and I know there has to be this algorithm somewhere in the Excel code.
Given a positive integer, return its corresponding column title as appear in an Excel sheet.
For example:
1 -> A
2 -> B
3 -> C
...
26 -> Z
27 -> AA
28 -> AB
| # encoding: UTF-8 | |
| require 'minitest/autorun' | |
| # Given a positive integer, return its corresponding column title as appear in an Excel sheet. | |
| # For example: | |
| # 1 -> A | |
| # 2 -> B | |
| # 3 -> C | |
| # ... | |
| # 26 -> Z | |
| # 27 -> AA | |
| # 28 -> AB | |
| ASCII_OFFSET_CONST = 64 | |
| ALPHABET_BASE = 26 | |
| def excel_column(col_number) | |
| return -1 unless | |
| col_number && col_number.respond_to?(:to_int) && col_number > 1 | |
| output_col = [] | |
| while col_number > 0 do | |
| output_col.unshift(((col_number % ALPHABET_BASE) + ASCII_OFFSET_CONST).chr) | |
| col_number = (col_number / ALPHABET_BASE).floor | |
| end | |
| output_col.join | |
| end | |
| describe "answer validation" do | |
| it "returns correct column encodings" do | |
| invalid_input = "I'm Invalid" | |
| assert_equal -1, | |
| excel_column(invalid_input), "should handle invalid input" | |
| invalid_input = -42 | |
| assert_equal -1, | |
| excel_column(invalid_input), "should handle invalid input" | |
| expected_answer = "BB" | |
| assert_equal expected_answer, | |
| excel_column(54), "Should give correct answer for BB" | |
| end | |
| end |