How do you approach Excel Sheet Column Number?

This is essentially a base-26 number system.

What is the time complexity of Excel Sheet Column Number?

Time complexity: O(n) - where n is the length of the string. Space complexity: O(1) - constant space.

What are common mistakes on Excel Sheet Column Number?

Overflowing at an intermediate step even though the final answer fits. Assuming a modulo is non-negative. In most languages -1 % n is negative, which breaks cyclic indexing. Testing floating-point values for exact equality where integer arithmetic would have been exact.

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Excel Sheet Column Number

EasyAlgorithms

Description

Given a string columnTitle that represents the column title as it appears in an Excel sheet, return its corresponding column number.

For example:

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...

Example 1

Input: columnTitle = "A"

Output: 1

Example 2

Input: columnTitle = "AB"

Output: 28

Example 3

Input: columnTitle = "ZY"

Output: 701

Constraints

- 1 <= columnTitle.length <= 7 - columnTitle consists only of uppercase English letters. - columnTitle is in the range ["A", "FXSHRXW"].

Excel Sheet Column Number: approach, complexity and pitfalls

An easy math problem, graded against 8 test cases (5 of them hidden).

The pattern: Math

Number theory, digit manipulation, and closed-form reasoning.

Reach for it when you see: Primes, digits, base conversion, or a problem with a formula hiding behind it.

If you are stuck

Show the 3-step hint ladder

This is essentially a base-26 number system.
Process the string from left to right, multiplying the running total by 26 each time.
The value of each character is its position in the alphabet (A=1, B=2, ..., Z=26).

The optimal approach

Show the approach: Base-26 Conversion

Treat the column title as a base-26 number where A=1, B=2, ..., Z=26. Process left to right, multiplying the accumulated result by 26 and adding the current character's value.

For example, "AB" = 1 * 26 + 2 = 28.

Time: O(n) - where n is the length of the string
Space: O(1) - constant space

The full reference solution in every supported language stays in the editor above - reveal it there once you have had a real attempt.

Common Math mistakes

These apply to the pattern as a whole, not just this problem.

Overflowing at an intermediate step even though the final answer fits.
Assuming a modulo is non-negative. In most languages `-1 % n` is negative, which breaks cyclic indexing.
Testing floating-point values for exact equality where integer arithmetic would have been exact.