Excel Column Number Conversion

In Excel, columns are labeled alphabetically, starting with 'A' for the first column, 'B' for the second, and so on. After 'Z', the columns continue with 'AA', 'AB', and so forth. This system is analogous to a base-26 numbering system where each letter represents a digit.

The challenge is to write a function that converts a given column title (as appears in an Excel sheet) into its corresponding column number.

Problem Statement:

You are given a string columnTitle that represents the column title as it appears in an Excel sheet. Your task is to return the corresponding column number.

Examples:

• Input: columnTitle = "A" Output: 1 Explanation: The first column is labeled as "A", so the corresponding number is 1.
• Input: columnTitle = "AB" Output: 28 Explanation: The column "AB" corresponds to the number 28 because it represents the 27th and 2nd positions in a base-26 system: 1×261+2×260=281 \times 26^1 + 2 \times 26^0 = 281×261+2×260=28.
• Input: columnTitle = "ZY" Output: 701 Explanation: The column "ZY" corresponds to the number 701 because it represents the 26th and 25th positions in a base-26 system: 26×261+25×260=70126 \times 26^1 + 25 \times 26^0 = 70126×261+25×260=701.

Constraints:

• The length of `columnTitle` is between 1 and 7 characters.
• `columnTitle` consists only of uppercase English letters.
• `columnTitle` is guaranteed to be within the valid range, from "A" to "FXSHRXW".

Approach:

To convert the Excel column title into its corresponding number, the solution treats the string as a base-26 number, where each letter contributes to the final number based on its position.

Steps to Solve:

1. Initialize a result variable to 0.
2. Iterate over each character in the string `columnTitle` from left to right.
3. For each character, calculate its corresponding value using the formula current_value = ord(char) - ord('A') + 1.
4. Update the result with `result = result * 26 + current_value`.
5. Continue this until all characters are processed.
6. Return the `result`.

This code efficiently converts the Excel column title into the corresponding column number by simulating how numbers are formed in a base-26 system, similar to how we handle decimal numbers.

Conclusion:

This problem is an excellent exercise in understanding how different number systems work and translating them into a computational format. The Excel column numbering system, though seemingly simple, offers an interesting challenge when converted to its numerical equivalent. The provided solution is both concise and efficient, ensuring that even for the longest valid column titles, the computation remains performant.