What is the time complexity of Excel Sheet Column Title?

The optimal solution has a time complexity of O(logN).

What is the space complexity of Excel Sheet Column Title?

The space complexity is O(logN).

What data structures are used to solve Excel Sheet Column Title?

This problem uses Math, String. Understanding these concepts is essential for solving this Easy problem efficiently.

What are the key insights for solving Excel Sheet Column Title?

Insight 1: The problem can be solved using a base-26 number system (similar to base-10, but with 26 digits). Each digit represents a letter from A to Z. Insight 2: Converting from base-26 requires repeated division by 26 and taking the remainder. The remainders represent the digits in the base-26 representation.

Which companies ask LeetCode 168. Excel Sheet Column Title in interviews?

This problem is frequently asked at Accenture, Oracle, Yext, Zenefits, Zoho.

JavaScript is required for the full interactive experience. However, all content is accessible without JavaScript.

Excel Sheet Column Title - LeetCode 168 Solution

Excel Sheet Column Title - Complete Solution Guide

Excel Sheet Column Title is LeetCode problem 168, a Easy level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

Given an integer columnNumber , return its corresponding column title as it appears in an Excel sheet . For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnNumber = 1 Output: "A" Example 2: Input: columnNumber = 28 Output: "AB" Example 3: Input: columnNumber = 701 Output: "ZY" Constraints: 1 <= columnNumber <= 2 31 - 1

Detailed Explanation

The problem asks you to convert a given integer representing a column number in an Excel sheet to its corresponding column title. Excel column titles are represented as letters: A, B, C... Z, AA, AB, etc. The input is an integer `columnNumber` (1 <= `columnNumber` <= 2<sup>31</sup> - 1), and the output is a string representing the Excel column title. For example, 1 corresponds to "A", 28 corresponds to "AB", and 701 corresponds to "ZY".

Solution Approach

The solution uses a base-26 conversion algorithm. The input integer `columnNumber` is repeatedly divided by 26. The remainder of each division represents a letter (A-Z) where 0 corresponds to Z, 1 corresponds to A, and so on. These letters are concatenated to form the final column title. The provided solutions differ slightly in how they handle the letter mapping and string building; some use string concatenation directly, while others use a StringBuilder (Java) for improved efficiency.

Step-by-Step Algorithm

Step 1: Initialize an empty string or StringBuilder to store the result.
Step 2: Repeat until `columnNumber` becomes 0:
Step 3: Decrement `columnNumber` by 1 (to adjust for 0-based indexing of A-Z).
Step 4: Calculate the remainder when `columnNumber` is divided by 26. This remainder represents the next letter in the column title. Convert the remainder to its corresponding letter (A-Z) using ASCII values (e.g., 'A' + remainder).
Step 5: Prepend (or append and later reverse) this letter to the result string.
Step 6: Update `columnNumber` by integer division with 26 (`columnNumber //= 26`).
Step 7: Return the result string.

Key Insights

Insight 1: The problem can be solved using a base-26 number system (similar to base-10, but with 26 digits). Each digit represents a letter from A to Z.
Insight 2: Converting from base-26 requires repeated division by 26 and taking the remainder. The remainders represent the digits in the base-26 representation.
Insight 3: The order of digits obtained from the remainders needs to be reversed to form the correct column title. (Or, string concatenation is done from left to right).

Complexity Analysis

Time Complexity: O(logN)

Space Complexity: O(logN)

Topics

This problem involves: Math, String.

Companies

Asked at: Accenture, Oracle, Yext, Zenefits, Zoho.

Excel Sheet Column Title | LeetCode 168

Easy

Math String

Time: O(logN)Space: O(logN)

Solution Code

Available in:

class Solution {
    public String convertToTitle(int columnNumber) {
        StringBuilder result = new StringBuilder();
        while (columnNumber > 0) {
            columnNumber--;
            result.append((char)('A' + columnNumber % 26));
            columnNumber /= 26;
        }
        return result.reverse().toString();
    }
}

View Full Solution on GitHubGitHub Solution View on LeetCodeLeetCode

Problem Info

Description

Problem 168: Excel Sheet Column Title - Detailed explanation and solution approaches.

Topics

Math String

Companies

AccentureOracleYextZenefitsZoho

Stats

Difficulty:Easy

Languages:4

Companies:5

Problem #:168

Problem Explanation

💡

Think Before You Code

🤔 Ask Yourself

→What is the input? What output do I need?
→Can I solve a smaller version of this problem first?
→What patterns have I seen in similar problems?

✏️ Try This First

Before looking at the solution, try to solve it on paper with a simple example!

🚀 Try on LeetCode

Solution Approach

📋

Step-by-Step Solution

7 steps

1
Step 1: Initialize an empty string or StringBuilder to store the result.
2
Step 2: Repeat until `columnNumber` becomes 0:
3
Step 3: Decrement `columnNumber` by 1 (to adjust for 0-based indexing of A-Z).
4
Step 4: Calculate the remainder when `columnNumber` is divided by 26. This remainder represents the next letter in the column title. Convert the remainder to its corresponding letter (A-Z) using ASCII values (e.g., 'A' + remainder).
5
Step 5: Prepend (or append and later reverse) this letter to the result string.
6
Step 6: Update `columnNumber` by integer division with 26 (`columnNumber //= 26`).
7
Step 7: Return the result string.

💡

Pro Tip for Students

Try tracing through each step with a small example on paper before coding. Understanding "why" each step happens is more important than memorizing the code!

⚡

Complexity Analysis

⏱️

Time Complexity

O(logN)

🚀 Logarithmic - Very efficient! Halves the problem each step.

💾

Space Complexity

O(logN)

🎯 Logarithmic space - Very memory efficient!

📝

Why?

The number of iterations in the while loop is proportional to the number of digits in the base-26 representation of the input number. The number of digits is approximately log<sub>26</sub>(N). The space used by the result string is also proportional to the number of digits.

📖New to Big O? Click to learn more

Big O Notation - Quick Guide

O(1)Best - Instant

O(log n)Excellent - Binary Search

O(n)Good - One loop

O(n log n)OK - Sorting

O(n²)Slow - Nested loops

O(2ⁿ)Very Slow - Recursion

Alternative Approaches

Recursive Approach

A recursive function could be used to achieve the same result. The base case would be when columnNumber is less than 26. Otherwise, recursively call the function for columnNumber // 26 and prepend the appropriate letter.

Time: O(logN)Space: O(logN) due to recursive call stack

Trade-offs: Recursive solution can be less efficient due to function call overhead compared to the iterative approach. However, it can be more concise.

✨

Key Insights

1Insight 1: The problem can be solved using a base-26 number system (similar to base-10, but with 26 digits). Each digit represents a letter from A to Z.
2Insight 2: Converting from base-26 requires repeated division by 26 and taking the remainder. The remainders represent the digits in the base-26 representation.
3Insight 3: The order of digits obtained from the remainders needs to be reversed to form the correct column title. (Or, string concatenation is done from left to right).

📚

Key Terms Explained

For Students

String

A sequence of characters. Like a word or sentence in programming!

Edge Cases

Edge case 1: When columnNumber is 1, the function should correctly return "A". The code handles this correctly by returning 'A' after the first iteration of the loop.
Edge case 2: When columnNumber is a multiple of 26 (e.g., 26, 52), the code correctly handles the transition to a new letter sequence (e.g., "Z", "AZ", etc.). The decrement before modulo operation ensures that the sequence is correct.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Incorrectly handling the base-26 conversion, particularly the mapping of remainders to letters and the order of concatenation. Forgetting to handle 0 as Z is a common error.

✗Common mistake 2: Forgetting to decrement `columnNumber` before the modulo operation, which will lead to an off-by-one error in the letter mapping. Inefficient string manipulation (using repeated concatenation in Python). StringBuilder in Java is much more efficient.

✅

Learning Tip

Every mistake is a learning opportunity! When you make an error, understand why it happened before moving on.

🌍

Where is This Used in Real Life?

💼Real-world scenario 1: Spreadsheet applications frequently use this type of column naming convention, making this conversion necessary for various data processing and manipulation tasks.

🏦Real-world scenario 2: In software that interacts with Excel files or other spreadsheet formats, this algorithm is often needed to translate between integer indices and the human-readable column names used in those files.

💡Understanding real-world applications helps you see the "why" behind algorithms. It's not just about passing interviews—these concepts power the apps and websites you use every day!

Author's Notes

💡 Key Insight

When dealing with arrays, always consider if sorting would simplify the problem. Many array problems have O(n) solutions using hash maps or two-pointer technique.

🎯 Interview Tip

Even for easy problems, discuss time and space complexity. Interviewers want to see you think analytically.

⚠️ Watch Out

Always test your solution with edge cases: empty input, single element, and boundary values.

Written by Saswata Mondal

Software Engineer • Algorithms Enthusiast • Interview Coach

👨‍💻

About the Author

👨‍💻

Saswata MondalAuthor400+ LC Problems

B.Tech CSE, IEM Kolkata | LeetCode Rating: 1672 (Top 15%)

Certified: IBM Java Developer, NPTEL Programming in Java

Last updated: November 16, 2024LeetCode Profile GitHub

This solution has been crafted based on my experience solving 400+ LeetCode problems. Each explanation is designed to help you understand the underlying concepts, not just memorize the code.

Community Tips & Insights

Try solving this without using extra space first. It's a great exercise for understanding the underlying pattern.

@CodeNinjaJul 13

In a real interview, always clarify constraints first. Ask about input size and value ranges.

@TechLeadJul 6

❓

Frequently Asked Questions

How do I handle string manipulation efficiently?

In languages with immutable strings (Java, Python, C#), use StringBuilder/list to avoid O(n) concatenation cost. Consider using character arrays for in-place modifications. For pattern matching, consider KMP or Rabin-Karp for O(n+m) complexity.

How should I approach easy-level algorithm problems?

Easy problems build foundational skills. Focus on: 1) Understanding the problem completely before coding, 2) Writing clean, readable code, 3) Handling all edge cases (empty input, single element, etc.), 4) Analyzing time and space complexity. Don't skip complexity analysis even for simple solutions.

How should I practice algorithm problems effectively?

Focus on understanding patterns rather than memorizing solutions. After solving a problem, review optimal solutions and understand the intuition. Group similar problems to recognize patterns. Practice explaining your approach out loud. Review problems after a few days to test retention.

What is the optimal approach for "Excel Sheet Column Title"?

For this easy-level Math problem, the key is to identify the core pattern. Analyze the input constraints to determine acceptable time complexity. Consider whether string techniques can optimize the solution. Always handle edge cases and validate your approach with examples before coding.

🤖 Need help with this problem?