Excel Sheet Column Number

Excel Sheet Column Number - Problem

Math String Easy

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

In Excel, columns are labeled as:

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

This is essentially converting from base-26 numbering system to decimal, where A=1, B=2, ..., Z=26.

Input & Output

Example 1 — Single Character

$ Input: columnTitle = "A"

› Output: 1

💡 Note: A is the first column, so it corresponds to column number 1

Example 2 — Two Characters

$ Input: columnTitle = "AB"

› Output: 28

💡 Note: A=1, B=2. Result = 1×26 + 2 = 28. This is column AB which comes after Z (26) and AA (27)

Example 3 — Last Single Character

$ Input: columnTitle = "Z"

› Output: 26

💡 Note: Z is the 26th letter, corresponding to column number 26

Constraints

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

Visualization

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Asked in

M Microsoft 45 G Google 30 a Amazon 25

The key insight is to treat Excel columns as a base-26 number system where A=1, B=2, ..., Z=26. Best approach is mathematical conversion in a single pass. Time: O(n), Space: O(1)

Common Approaches

✓ Brute Force - Character by Character

⏱️ Time: O(n) Space: O(1)

Process each character from left to right, converting each letter to its numeric value (A=1, B=2, etc.) and building the result by multiplying the current result by 26 and adding the new digit.

Mathematical Base Conversion

⏱️ Time: O(n) Space: O(1)

Treat the Excel column as a base-26 number system where each position represents a power of 26, and convert directly to decimal using the positional value formula.

Brute Force - Character by Character — Algorithm Steps

Step 1: Initialize result to 0
Step 2: For each character, convert to number (A=1, B=2, ...)
Step 3: Multiply current result by 26 and add the character value

Visualization

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Step-by-Step Walkthrough

Initialize

Start with result = 0

Process Each Char

Multiply by 26 and add character value

Final Result

Complete column number

Code -

solution.c — C

#include <stdio.h>
#include <string.h>

int solution(char* columnTitle) {
    int result = 0;
    int len = strlen(columnTitle);
    for (int i = 0; i < len; i++) {
        result = result * 26 + (columnTitle[i] - 'A' + 1);
    }
    return result;
}

int main() {
    char columnTitle[10];
    fgets(columnTitle, sizeof(columnTitle), stdin);
    columnTitle[strcspn(columnTitle, "\n")] = 0;
    int result = solution(columnTitle);
    printf("%d\n", result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through all n characters in the string

✓ Linear Growth

Space Complexity

O(1)

Only using a constant amount of extra variables

✓ Linear Space

180.0K Views

Medium Frequency

~15 min Avg. Time

2.1K Likes

Ln 1, Col 1

Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Brute Force - Character by Character — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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