Excel Sheet Column Number

Excel column titles use a unique system where A=1, B=2, ..., Z=26. After Z, the system continues with AA=27, AB=28, and so on. This challenge asks you to write a function that converts a given Excel column title (represented as a string) into its corresponding column number. This is useful for automating spreadsheet tasks and understanding Excel's internal representation of columns.

Problem Description

You are given a string representing an Excel column title. Your task is to convert this string into its corresponding integer column number. The string will consist of uppercase English letters ('A' to 'Z'). The column title can be of any length, representing columns beyond 'Z'.

What needs to be achieved:

• Write a function that takes a string (Excel column title) as input.
• The function should return an integer representing the corresponding column number.

Key requirements:

• The input string will only contain uppercase English letters.
• The function must handle column titles of any length.
• The function must correctly convert the column title to its integer representation.

Expected behavior:

The function should return the correct column number for any valid Excel column title.

Edge cases to consider:

• Empty string: Should return 0 (or handle as an error, depending on desired behavior - specify in notes).
• Single-letter column titles (A, B, ..., Z).
• Multi-letter column titles (AA, AB, ..., AZ, BA, ..., ZZ, AAA, etc.).
• Very long column titles (though realistically, Excel has limits, consider the theoretical possibility).

Examples

Example 1:

Input: "A"
Output: 1
Explanation: The first column is represented by 'A', which corresponds to the number 1.

Example 2:

Input: "AB"
Output: 28
Explanation: 'A' is 1 and 'B' is 2.  1 * 26^1 + 2 * 26^0 = 1 * 26 + 2 * 1 = 26 + 2 = 28.

Example 3:

Input: "ZY"
Output: 701
Explanation: 'Z' is 26 and 'Y' is 25. 26 * 26^1 + 25 * 26^0 = 26 * 26 + 25 * 1 = 676 + 25 = 701.

Example 4:

Input: "AAA"
Output: 703
Explanation: 'A' is 1. 1 * 26^2 + 1 * 26^1 + 1 * 26^0 = 1 * 676 + 1 * 26 + 1 * 1 = 676 + 26 + 1 = 703.

Constraints

• The input string will have a length between 1 and 1000 (inclusive).
• The input string will only contain uppercase English letters ('A' to 'Z').
• The column number will be within the range of a 32-bit integer.
• Performance: The solution should complete within a reasonable time (e.g., less than 1 second) for the maximum input length.

Notes

• Consider using a base-26 conversion approach. Each letter represents a digit in base-26, where 'A' is 1, 'B' is 2, ..., 'Z' is 26.
• Iterate through the string from right to left, multiplying each digit by the appropriate power of 26.
• Handle the empty string case appropriately. Returning 0 is a reasonable default.
• The problem can be solved efficiently with a single pass through the string.
• Think about how to handle the conversion from character to numerical value (A=1, B=2, etc.). The ASCII value of a character can be helpful.