Add solution for Challenge 21 by 4m4x

[4m4x]

Challenge 21 Solution

Submitted by: @4m4x
Challenge: Challenge 21

Description

This PR contains my solution for Challenge 21.

Changes

• Added solution file to challenge-21/submissions/4m4x/solution-template.go

Testing

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

Thank you for reviewing my submission! 🚀

[coderabbitai]

Walkthrough

A new Go file is added to the Challenge 21 submission directory containing three binary search implementations: a non-recursive BinarySearch function, a recursive BinarySearchRecursive function, and a FindInsertPosition function for determining insertion indices in sorted arrays. The file includes a main function with example usage and no external dependencies.

Changes

Cohort / File(s)	Summary
Binary Search Solution challenge-21/submissions/4m4x/solution-template.go	Added three public functions: BinarySearch (iterative search returning index or -1), BinarySearchRecursive (recursive variant with explicit left/right bounds), and FindInsertPosition (determines insertion position in sorted array). Includes main function with example usage and Russian implementation comments.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

• Standard algorithm implementations with straightforward logic
• Single file addition with no cross-file dependencies
• Main complexity is verifying correctness of binary search boundary handling (particularly in recursive and insertion position variants)

Possibly related PRs

• Add solution for Challenge 21 by rodney-b #707: Adds the same three binary search functions (BinarySearch, BinarySearchRecursive, FindInsertPosition) with a demo main in a solution-template.go for Challenge 21.
• Add solution for Challenge 21 by kiramux #670: Implements the same three exported binary-search utilities in separate submission files for Challenge 21.
• Add solution for Challenge 21 by iamsurajmandal #714: Adds the same three functions implementing equivalent binary-search logic in solution-template.go for a different submission directory under Challenge 21.

Pre-merge checks

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding a solution for Challenge 21 by the user 4m4x, which matches the file addition and PR objectives.
Description check	✅ Passed	The description is relevant to the changeset, clearly explaining that it contains a Challenge 21 solution submission with the file path and testing verification.

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Actionable comments posted: 0

🧹 Nitpick comments (2)

challenge-21/submissions/4m4x/solution-template.go (2)

26-48: Iterative binary search implementation looks correct; only minor style nits

The search bounds and termination condition are correct and handle empty slices safely. The only small nits are:

• The early len(arr) == 0 check is redundant because the for low <= high loop with high := len(arr)-1 already covers the empty case.
• The inline comment is in Russian; you might consider rewriting it in English so the entire team can easily read it.

Both are purely optional cleanups.

---

50-70: Recursive binary search is correct; consider tightening base cases and parameter style

Logic and bounds handling look good and are safe for empty slices. You can make it slightly clearer and more idiomatic by:

• Combining the empty-slice and left > right checks into a single base case before computing mid.
• Grouping parameter types for left and right.

For example:

-func BinarySearchRecursive(arr []int, target int, left int, right int) int {
-	if len(arr) == 0 {
-		return -1
-	}
-
-	mid := (left + right) / 2
-
-	if left > right {
-		return -1
-	}
+func BinarySearchRecursive(arr []int, target int, left, right int) int {
+	if len(arr) == 0 || left > right {
+		return -1
+	}
+
+	mid := (left + right) / 2

The rest of the function can stay as‑is. This keeps the exit conditions up front and avoids computing mid when you already know the search is done.

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between ca8ea29 and a19750d.

📒 Files selected for processing (1)

• challenge-21/submissions/4m4x/solution-template.go (1 hunks)

🔇 Additional comments (2)

challenge-21/submissions/4m4x/solution-template.go (2)

7-24: Main function is clear and useful for local validation

The sample data and prints exercise all three functions and make it easy to sanity‑check behavior; no changes needed here.

---

72-86: Insert-position finder matches lower_bound semantics and handles edge cases

The loop invariant and final return left give the correct insertion index for all cases, including empty slices, targets smaller than all elements, and larger than all elements. Implementation is clean and idiomatic.