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Nov 18, 2025
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Add solution for Challenge 21 by yz4230 #747

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78 changes: 78 additions & 0 deletions challenge-21/submissions/yz4230/solution-template.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,78 @@
package main

import (
"fmt"
)

func main() {
// Example sorted array for testing
arr := []int{1, 3, 5, 7, 9, 11, 13, 15, 17, 19}

// Test binary search
target := 7
index := BinarySearch(arr, target)
fmt.Printf("BinarySearch: %d found at index %d\n", target, index)

// Test recursive binary search
recursiveIndex := BinarySearchRecursive(arr, target, 0, len(arr)-1)
fmt.Printf("BinarySearchRecursive: %d found at index %d\n", target, recursiveIndex)

// Test find insert position
insertTarget := 8
insertPos := FindInsertPosition(arr, insertTarget)
fmt.Printf("FindInsertPosition: %d should be inserted at index %d\n", insertTarget, insertPos)
}

// BinarySearch performs a standard binary search to find the target in the sorted array.
// Returns the index of the target if found, or -1 if not found.
func BinarySearch(arr []int, target int) int {
left, right := 0, len(arr)
for left < right {
mid := (right - left) / 2 + left
midv := arr[mid]
if target < midv {
right = mid
} else if midv < target {
left = mid + 1
} else {
return mid
}
}
return -1
}
Comment on lines +28 to +42
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@coderabbitai coderabbitai bot Nov 16, 2025

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⚠️ Potential issue | 🟡 Minor

Inconsistent interval convention with recursive variant.

The iterative BinarySearch uses a half-open interval [left, right) (initialized with right := len(arr)), while BinarySearchRecursive uses a closed interval [left, right] (called with len(arr)-1). Both implementations are correct individually, but the inconsistency can confuse maintainers.

Consider standardizing on one convention across both functions for better code consistency.

🤖 Prompt for AI Agents 
challenge-21/submissions/yz4230/solution-template.go lines 28-42: the iterative
BinarySearch uses a half-open interval [left,right) (right := len(arr)) while
the recursive variant uses a closed interval [left,right] (invoked with
len(arr)-1), causing inconsistency; pick one convention and make both functions
match — either change the iterative function to use closed interval (initialize
right := len(arr)-1, adjust loop condition to left <= right and update pointers
accordingly) or change the recursive variant to use half-open bounds (accept
right as len(arr) and treat right as exclusive in the recursion), and update all
comparisons/indices and base cases to follow the chosen convention consistently.


// BinarySearchRecursive performs binary search using recursion.
// Returns the index of the target if found, or -1 if not found.
func BinarySearchRecursive(arr []int, target int, left int, right int) int {
if left > right {
return -1
}

mid := (right - left) / 2 + left
midv := arr[mid]
if target < midv {
return BinarySearchRecursive(arr, target, left, mid-1)
} else if midv < target {
return BinarySearchRecursive(arr, target, mid+1, right)
} else {
return mid
}
}

// FindInsertPosition returns the index where the target should be inserted
// to maintain the sorted order of the array.
func FindInsertPosition(arr []int, target int) int {
left, right := 0, len(arr)
for left < right {
mid := (right - left) / 2 + left
midv := arr[mid]
if target < midv {
right = mid
} else if midv < target {
left = mid + 1
} else {
return mid
}
}
return left
}
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