Writing good commit messages in Git - Time & Space Complexity

Time Complexity: Writing good commit messages

O(n)

Understanding Time Complexity

We want to understand how the time to write commit messages changes as the number of commits grows.

How does the effort scale when making many commits?

Scenario Under Consideration

Analyze the time complexity of writing commit messages for multiple commits.

git add .
git commit -m "Fix typo in README"
git add .
git commit -m "Add new feature"
git add .
git commit -m "Update config"

This snippet shows making three commits, each with a message describing the change.

Identify Repeating Operations

Each commit requires writing a message.

• Primary operation: Writing a commit message
• How many times: Once per commit

How Execution Grows With Input

As the number of commits increases, the total time to write messages grows proportionally.

Input Size (n commits)	Approx. Operations (messages written)
10	10
100	100
1000	1000

Pattern observation: The effort grows linearly with the number of commits.

Final Time Complexity

Time Complexity: O(n)

This means the time to write commit messages grows directly with the number of commits.

Common Mistake

[X] Wrong: "Writing commit messages takes the same time no matter how many commits I make."

[OK] Correct: Each commit needs its own message, so more commits mean more messages and more time.

Interview Connect

Understanding how tasks scale with input size helps you explain your work clearly and shows you think about efficiency in real projects.

Self-Check

"What if you used a single commit for many changes instead of many commits? How would the time complexity change?"

Practice

1. What is the main purpose of a good commit message in Git?

easy

A. To list all files changed in the commit

B. To explain what changes were made and why

C. To include the entire code change in the message

D. To write a long story about the project history

Solution

1. Step 1: Understand the role of commit messages

   Commit messages should clearly explain what was changed and why, helping others understand the purpose.

2. Step 2: Identify the best option

   To explain what changes were made and why correctly states the purpose, while others focus on irrelevant or incorrect details.

3. Final Answer:

   To explain what changes were made and why -> Option B

4. Quick Check:

   Good commit message = explain what and why [OK]

Hint: Focus on explaining changes and reasons, not details [OK]

Common Mistakes:

• Listing files instead of explaining changes
• Writing too much unrelated history
• Including code in the message

2. Which of the following is the correct format for a good Git commit message?

easy

A. A message with only emojis

B. A long paragraph without a summary line

C. Only a list of changed files

D. A short summary line followed by a blank line and detailed explanation

Solution

1. Step 1: Recall Git commit message format

   A good commit message starts with a short summary line, then a blank line, then optional details.

2. Step 2: Match options to format

   A short summary line followed by a blank line and detailed explanation matches this format exactly; others do not follow best practices.

3. Final Answer:

   A short summary line followed by a blank line and detailed explanation -> Option D

4. Quick Check:

   Summary line + blank line + details = correct format [OK]

Hint: Use a short summary line, then details after a blank line [OK]

Common Mistakes:

• Skipping the blank line between summary and details
• Writing only a long paragraph
• Using emojis without explanation

3. Given this commit message:
Fix login bug
What is missing to make it a good commit message?

medium

A. A detailed explanation of why the bug was fixed

B. A list of all files changed

C. A longer summary line

D. The author's email

Solution

1. Step 1: Analyze the commit message content

   The message only has a short summary but lacks explanation of why the bug was fixed.

2. Step 2: Identify what improves clarity

   Adding a detailed explanation helps others understand the reason behind the fix.

3. Final Answer:

   A detailed explanation of why the bug was fixed -> Option A

4. Quick Check:

   Good message = what + why, missing why here [OK]

Hint: Add why the change was made, not just what [OK]

Common Mistakes:

• Only writing a short summary
• Listing files instead of explanation
• Adding unrelated info like author email

4. You wrote this commit message:
fix login bug
What is the main problem with this message?

medium

A. It includes a blank line after the summary

B. It is too long and detailed

C. It uses lowercase and lacks a capitalized summary

D. It uses past tense instead of present tense

Solution

1. Step 1: Check capitalization in commit messages

   Good commit messages start with a capitalized summary line.

2. Step 2: Evaluate the given message

   The message starts with lowercase 'fix', which is not recommended.

3. Final Answer:

   It uses lowercase and lacks a capitalized summary -> Option C

4. Quick Check:

   Summary line should start capitalized [OK]

Hint: Always capitalize the first letter of the summary line [OK]

Common Mistakes:

• Starting summary with lowercase letter
• Making summary too long
• Ignoring tense conventions

5. You want to write a commit message for adding a new feature that improves search speed by caching results. Which commit message is best?

hard

A. Add caching to improve search speed

Implemented a cache layer to store recent search results, reducing response time.

B. Improved search speed by adding cache

Cache added.

C. Added cache

This commit adds cache.

D. Fix search speed

Cache implemented.

Solution

1. Step 1: Evaluate clarity and detail in options

   Add caching to improve search speed Implemented a cache layer to store recent search results, reducing response time. has a clear summary and detailed explanation of what and why.

2. Step 2: Compare other options

   The other options are vague, use incorrect tense or verbs (such as 'Fix' for a new feature), or lack detailed explanation.

3. Final Answer:

   Add caching to improve search speed Implemented a cache layer to store recent search results, reducing response time. -> Option A

4. Quick Check:

   Clear summary + detailed why = best commit message [OK]

Hint: Use clear summary and explain why change matters [OK]

Common Mistakes:

• Using vague summaries
• Wrong verbs like 'Fix' for new features
• Too short or unclear explanations