git restore to discard working changes - Time & Space Complexity

Time Complexity: git restore to discard working changes

O(n)

Understanding Time Complexity

We want to understand how the time to discard changes in files grows as the number of files changes.

How does git handle undoing changes when many files are involved?

Scenario Under Consideration

Analyze the time complexity of the following git command.

git restore file1.txt file2.txt file3.txt

# or to discard all changes:
git restore .

This command discards changes in the working directory by restoring files to their last committed state.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Restoring each file by reading its last committed version and overwriting the working copy.
• How many times: Once per file specified or once per changed file if restoring all.

How Execution Grows With Input

As the number of files to restore increases, the total work grows roughly in direct proportion.

Input Size (n files)	Approx. Operations
10	10 file restores
100	100 file restores
1000	1000 file restores

Pattern observation: Doubling the number of files doubles the work needed to restore them.

Final Time Complexity

Time Complexity: O(n)

This means the time to discard changes grows linearly with the number of files you restore.

Common Mistake

[X] Wrong: "Restoring many files happens instantly no matter how many files there are."

[OK] Correct: Each file must be individually restored, so more files mean more work and more time.

Interview Connect

Understanding how commands scale with input size helps you explain performance and make better decisions in real projects.

Self-Check

"What if we used git restore with a large directory instead of individual files? How would the time complexity change?"

Practice

1. What does the command git restore <filename> do in a Git repository?

easy

A. It permanently deletes the specified file from the repository history.

B. It discards changes in the specified file and restores it to the last committed state.

C. It stages the specified file for the next commit.

D. It creates a new branch with the name of the specified file.

Solution

1. Step 1: Understand the purpose of git restore

   The git restore command is used to undo changes in the working directory before committing.

2. Step 2: Effect on the specified file

   Using git restore <filename> resets the file to its last committed state, discarding any edits made since then.

3. Final Answer:

   It discards changes in the specified file and restores it to the last committed state. -> Option B

4. Quick Check:

   Undo changes = git restore [OK]

Hint: Use git restore to undo file edits before commit [OK]

Common Mistakes:

• Confusing restore with delete or branch creation
• Thinking it stages files instead of discarding changes
• Assuming it affects commit history

2. Which of the following is the correct syntax to discard changes in a file named app.js using git restore?

easy

A. git restore app.js

B. git restore --discard app.js

C. git restore -d app.js

D. git restore --reset app.js

Solution

1. Step 1: Recall the basic syntax of git restore

   The command to discard changes in a file is simply git restore <filename> without extra flags.

2. Step 2: Check the options given

   Options B, C, and D use incorrect or non-existent flags. Only git restore app.js uses the correct syntax.

3. Final Answer:

   git restore app.js -> Option A

4. Quick Check:

   Correct syntax = git restore filename [OK]

Hint: Use git restore filename without extra flags to discard changes [OK]

Common Mistakes:

• Adding unnecessary flags like --discard or --reset
• Using shorthand flags that don't exist
• Confusing git restore with git reset

3. Given the following sequence of commands in a Git repository:

echo 'Hello' > file.txt
git add file.txt
echo 'World' >> file.txt
git restore file.txt
cat file.txt

What will be the output of cat file.txt?

medium

A. Hello

B. World

C. Hello\nWorld

D. file.txt: No such file or directory

Solution

1. Step 1: Understand the commands before restore

   First, 'Hello' is written to file.txt and staged. Then 'World' is appended but not staged.

2. Step 2: Effect of git restore on file.txt

   The git restore file.txt discards the unstaged changes, reverting file.txt to the last staged (or committed) state which contains only 'Hello'.

3. Step 3: Output of cat file.txt

   After restore, file.txt contains only 'Hello'. So, cat file.txt outputs 'Hello'.

4. Final Answer:

   Hello -> Option A

5. Quick Check:

   Restore discards unstaged changes = Hello [OK]

Hint: Restore resets file to last staged or committed state [OK]

Common Mistakes:

• Assuming restore keeps appended changes
• Confusing staged and unstaged changes
• Expecting both lines to appear after restore

4. You ran git restore file.txt but your changes were not discarded. What is the most likely reason?

medium

A. Git restore only works on new files, not modified ones.

B. The file was already committed and has no changes to discard.

C. You used the wrong filename in the command.

D. You have staged the changes, so restore does not affect them by default.

Solution

1. Step 1: Understand git restore behavior with staged changes

   By default, git restore <file> only discards unstaged changes. Staged changes remain unless you add the --staged flag.

2. Step 2: Analyze why changes were not discarded

   If changes were staged, running restore without --staged won't discard them, so the file appears unchanged.

3. Final Answer:

   You have staged the changes, so restore does not affect them by default. -> Option D

4. Quick Check:

   Restore ignores staged changes unless --staged used [OK]

Hint: Use --staged to discard staged changes with git restore [OK]

Common Mistakes:

• Assuming restore discards staged changes without flags
• Thinking restore works only on new files
• Not checking if filename is correct

5. You have modified three files: index.html, style.css, and script.js. You staged index.html and style.css but want to discard only the unstaged changes in style.css and script.js. Which command will achieve this?

hard

A. git restore --discard style.css script.js

B. git restore --staged style.css script.js

C. git restore style.css script.js

D. git restore --staged style.css && git restore script.js

Solution

1. Step 1: Identify which changes to discard

   You want to discard unstaged changes in style.css and script.js. Staged changes should remain.

2. Step 2: Choose the correct git restore command

   git restore --discard style.css script.js uses invalid --discard flag. Options B and C use --staged which would discard staged changes, which is not desired. git restore style.css script.js discards unstaged changes only.

3. Final Answer:

   git restore style.css script.js -> Option C

4. Quick Check:

   Restore without --staged discards unstaged changes [OK]

Hint: Restore files without --staged to discard only unstaged changes [OK]

Common Mistakes:

• Using --staged and discarding staged changes accidentally
• Running separate commands unnecessarily
• Using invalid flags like --discard