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Looks like a simple base conversion until you realize it's not quite base-26 because there's no zero.
Treat the column title as a base-26 number where 'A' maps to 1 and 'Z' to 26, then process the string from left to right, accumulating the result by multiplying the current total by 26 and adding the value of the current character. This is analogous to converting a hexadecimal string to decimal, but with a 1-indexed alphabet.
Pro tip: Mention that this is essentially a base-26 conversion with a 1-indexed alphabet, and note that the reverse problem (number to title) uses a similar but slightly trickier approach due to the lack of a zero digit. This shows you understand the underlying number system and can handle edge cases.
Confirm that 'A' corresponds to 1, 'B' to 2, ..., 'Z' to 26, and that the string is read from left to right with the leftmost character being the most significant digit.
Set a variable (e.g., result) to 0 to accumulate the final column number.
For each character in the string, compute its value as (char - 'A' + 1), then update result = result * 26 + value.
After processing all characters, return the accumulated result as the column number.
State that the time complexity is O(n) where n is the length of the string, and space complexity is O(1) as only a constant amount of extra space is used.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.