Add solution for Challenge 21 by yz4230

[yz4230]

Challenge 21 Solution

Submitted by: @yz4230
Challenge: Challenge 21

Description

This PR contains my solution for Challenge 21.

Changes

• Added solution file to challenge-21/submissions/yz4230/solution-template.go

Testing

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

Thank you for reviewing my submission! 🚀

[coderabbitai]

Walkthrough

This pull request adds a new Go file containing binary search implementations for challenge-21. The file includes iterative binary search, recursive binary search, and a function to find insertion positions in sorted arrays, along with a demonstration main function that tests these implementations.

Changes

Cohort / File(s)	Summary
Binary Search Implementation challenge-21/submissions/yz4230/solution-template.go	New file added with three binary search functions: BinarySearch (iterative), BinarySearchRecursive (recursive), and FindInsertPosition (insertion position finder), plus a test-driven main function.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Verify correctness of iterative and recursive binary search logic (boundary conditions, mid-point calculations)
• Confirm FindInsertPosition correctly returns existing indices or proper insertion points
• Review main function test cases for adequate coverage

Possibly related PRs

• #747: Adds the identical file and functions (BinarySearch, BinarySearchRecursive, FindInsertPosition) to the same submission path
• #714: Adds the same Go search utility functions in a different challenge-21 submission file
• #707: Adds identical binary search functions with the same signatures in another solution-template Go file

Pre-merge checks

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% 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 directly summarizes the main change: adding a solution file for Challenge 21 by user yz4230, which aligns with the changeset.
Description check	✅ Passed	The description is directly related to the changeset, explaining the Challenge 21 solution submission and listing the added file.

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Actionable comments posted: 0

🧹 Nitpick comments (1)

challenge-21/submissions/yz4230/solution-template.go (1)

62-78: FindInsertPosition is correct; consider reducing duplication with BinarySearch

The insertion-index logic over [left, right) is correct for all targets (including before-first, after-last, and duplicates), and returning left on miss preserves sorted order. You could optionally factor the shared binary-search loop into a helper (e.g., a lower-bound function) and implement BinarySearch in terms of it to avoid duplicating nearly identical loops.

📜 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 bf1bfdf.

📒 Files selected for processing (1)

• challenge-21/submissions/yz4230/solution-template.go (1 hunks)

🔇 Additional comments (3)

challenge-21/submissions/yz4230/solution-template.go (3)

7-24: Sample main correctly exercises all search helpers

The demo covers both search variants and the insert-position helper with representative inputs; no functional issues here.

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26-42: Iterative BinarySearch is correct and handles edge cases well

Logic over a half-open interval [left, right) with a safe mid calculation is sound, including for empty slices and out-of-range targets; it returns -1 exactly when not found.

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44-60: Recursive BinarySearchRecursive implementation is logically sound

Closed-interval [left, right] handling with the left > right base case avoids out-of-bounds access and correctly terminates for all cases (including empty slices when called with right = len(arr)-1).