Excel Sheet Column Number

LeetCode 171 | Difficulty: Easy

Easy

Problem Description

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
...
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"]`.

Topics: Math, String

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Approach

Mathematical

Look for mathematical patterns or formulas. Consider: modular arithmetic, GCD/LCM, prime factorization, combinatorics, or geometric properties.

When to use

Problems with clear mathematical structure, counting, number properties.

String Processing

Consider character frequency counts, two-pointer approaches, or building strings efficiently. For pattern matching, think about KMP or rolling hash. For palindromes, expand from center or use DP.

When to use

Anagram detection, palindrome checking, string transformation, pattern matching.

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Solutions

Solution 1: C# (Best: 76 ms)

Metric	Value
Runtime	76 ms
Memory	36 MB
Date	2022-02-22

Solution

public class Solution {
    public int TitleToNumber(string s) {
    int result=0, len = s.Length;
    for (int i = 0; i <len ; i++)
    {
        result = (result*26) + (s[i]-'A'+1);
    }
    return result;
    }
}

📜 2 more C# submission(s)

Submission (2022-02-22) — 103 ms, 36.5 MB

public class Solution {
    public int TitleToNumber(string s) {
    int result=0;
    for (int i = 0; i <s.Length ; i++)
    {
        result = (result*26) + (s[i]-'A'+1);
    }
    return result;
    }
}

Submission (2018-03-30) — 336 ms, N/A

public class Solution {
    public int TitleToNumber(string s) {
    int result=0;
    for (int i = 0; i <s.Length ; i++)
    {
        result = (result*26) + (s[i]-'A'+1);
    }
    return result;
    }
}

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Complexity Analysis

Approach	Time	Space
Solution	$O(n)$	$O(1) to O(n)$

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Interview Tips

Key Points

• Start by clarifying edge cases: empty input, single element, all duplicates.