Add solution for Challenge 2 by Mxn-ptr

[Mxn-ptr]

Challenge 2 Solution

Submitted by: @Mxn-ptr
Challenge: Challenge 2

Description

This PR contains my solution for Challenge 2.

Changes

• Added solution file to challenge-2/submissions/Mxn-ptr/solution-template.go

Testing

• Solution passes all test cases
• Code follows Go best practices

Thank you for reviewing my submission! 🚀

[coderabbitai]

Walkthrough

Adds a new Go solution file containing a public ReverseString function that reverses input strings by converting to runes, swapping in-place, and returning the result. Includes a main function that reads a line from standard input, invokes the function, and prints the reversed string.

Changes

Cohort / File(s)	Summary
String Reversal Solution challenge-2/submissions/Mxn-ptr/solution-template.go	Introduces ReverseString(s string) string function implementing in-place rune-slice reversal, with main function wiring for stdin/stdout operations.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly related PRs

• Add solution for Challenge 2 by maikreyes #916: Implements the same ReverseString function with rune-swap in-place logic in a different submission directory.
• Add solution for Challenge 2 by ansmonjol #752: Adds identical ReverseString function and main wiring in challenge-2 submissions using rune-slice in-place swapping.
• Add solution for Challenge 2 by goholic #1194: Adds the same exported ReverseString(s string) string function for string reversal via rune-swap in different submission files.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding a solution file for Challenge 2 by the contributor Mxn-ptr.
Description check	✅ Passed	The description is directly related to the changeset, explaining that it contains a Challenge 2 solution submission with details about the added file and testing checklist.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@challenge-2/submissions/Mxn-ptr/solution-template.go`:
- Around line 9-20: The main function currently uses bufio.NewScanner and calls
scanner.Scan() without checking for scanner.Err() and without increasing the
default 64KB token limit; update main to configure the scanner buffer (via
scanner.Buffer with a larger max token size, e.g. ~1MB), then use an explicit
Scan() check and handle errors by calling scanner.Err() when Scan() returns
false (log or return on error) before calling ReverseString; reference scanner
:= bufio.NewScanner(os.Stdin), scanner.Buffer(...), scanner.Scan() and
scanner.Err() when making the change.

[coderabbitai]

⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🌐 Web query:

bufio.Scanner token size limit default buffer Go 1.22 error handling Scan Err

💡 Result:

• Default token size limit (Go 1.22 bufio.Scanner): MaxScanTokenSize = 64 * 1024 (65,536 bytes). In practice, the actual max token may be slightly smaller because the buffer may need to hold delimiters (e.g., newline). [1][2]
• What happens when a token is too large: Scan() stops and Err() returns bufio.ErrTooLong (error string: "bufio.Scanner: token too long"). Scanners do not return truncated tokens. [2][3]
• How to handle errors correctly:

  s := bufio.NewScanner(r)
  for s.Scan() {
      line := s.Text()
      _ = line
  }
  if err := s.Err(); err != nil {
      // err could be bufio.ErrTooLong or an underlying I/O error
      log.Fatal(err)
  }

  Scanning that ends at EOF is not an error (Err() is nil). [1][3]
• How to increase the limit: call Buffer before the first Scan() to set an initial buffer and the maximum token size. [1]

  s := bufio.NewScanner(r)
  buf := make([]byte, 64*1024)
  s.Buffer(buf, 1024*1024) // allow up to 1 MiB tokens

• If you need very long tokens or more control: prefer bufio.Reader (the docs explicitly recommend it for large tokens / more control). [3]

Sources:
[1] Go bufio docs (Scanner.Buffer, default uses MaxScanTokenSize) (pkg.go.dev)
[2] MaxScanTokenSize value and note about actual maximum token size (docs.go101.org)
[3] Scanner stopping conditions; ErrTooLong; recommendation to use bufio.Reader (go.pact.im)

Citations:

• 1: https://pkg.go.dev/bufio%40go1.25.4?utm_source=openai
• 2: https://docs.go101.org/std/pkg/bufio.html?utm_source=openai
• 3: https://go.pact.im/doc/pkg/bufio.html?utm_source=openai

---

Add error handling for scanner failures and increase token buffer limit.

bufio.Scanner has a default token-size limit of 64 KB. When Scan() returns false due to a token exceeding this limit or an I/O error, the code currently proceeds without checking Err(), ignoring the failure. Add error handling and increase the buffer to ensure long inputs and I/O errors are caught.

🔧 Suggested fix

 func main() {
 	// Read input from standard input
 	scanner := bufio.NewScanner(os.Stdin)
-	if scanner.Scan() {
-		input := scanner.Text()
+	// Increase buffer to handle longer lines if needed
+	scanner.Buffer(make([]byte, 1024), 1024*1024)
+	if !scanner.Scan() {
+		if err := scanner.Err(); err != nil {
+			fmt.Fprintln(os.Stderr, "input error:", err)
+			os.Exit(1)
+		}
+		return
+	}
+	input := scanner.Text()
 
-		// Call the ReverseString function
-		output := ReverseString(input)
+	// Call the ReverseString function
+	output := ReverseString(input)
 
-		// Print the result
-		fmt.Println(output)
-	}
+	// Print the result
+	fmt.Println(output)
 }

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	func main() {
	// Read input from standard input
	scanner := bufio.NewScanner(os.Stdin)
	if scanner.Scan() {
	input := scanner.Text()
	// Call the ReverseString function
	output := ReverseString(input)
	// Print the result
	fmt.Println(output)
	}
	func main() {
	// Read input from standard input
	scanner := bufio.NewScanner(os.Stdin)
	// Increase buffer to handle longer lines if needed
	scanner.Buffer(make([]byte, 1024), 1024*1024)
	if !scanner.Scan() {
	if err := scanner.Err(); err != nil {
	fmt.Fprintln(os.Stderr, "input error:", err)
	os.Exit(1)
	}
	return
	}
	input := scanner.Text()
	// Call the ReverseString function
	output := ReverseString(input)
	// Print the result
	fmt.Println(output)
	}

🤖 Prompt for AI Agents

In `@challenge-2/submissions/Mxn-ptr/solution-template.go` around lines 9 - 20,
The main function currently uses bufio.NewScanner and calls scanner.Scan()
without checking for scanner.Err() and without increasing the default 64KB token
limit; update main to configure the scanner buffer (via scanner.Buffer with a
larger max token size, e.g. ~1MB), then use an explicit Scan() check and handle
errors by calling scanner.Err() when Scan() returns false (log or return on
error) before calling ReverseString; reference scanner :=
bufio.NewScanner(os.Stdin), scanner.Buffer(...), scanner.Scan() and
scanner.Err() when making the change.