Excel Sheet Column Number — LeetCode 171 Python Solution

The problem

Given a string columnTitle that represents the column title as appears in an Excel sheet, return its corresponding column number. For example: A -> 1 B -> 2 C -> 3 ...

Example

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

Python solution

class Solution:
    def titleToNumber(self, columnTitle: str) -> int:
        ans = 0
        for c in map(ord, columnTitle):
            ans = ans * 26 + c - ord("A") + 1
        return ans

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 171. Excel Sheet Column Number is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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