goLogic errorMedium

Negative modulo index out of range in hash bucket

Time: 0:00

BugFind the bug and fix the code

What it should do

Calculate bucket index for a hash value within array size. Example: getHashBucket(-5, 4) -> 3

What happens instead

panic: runtime error: index out of range [-1] with length 4

package main

import "fmt"

func getHashBucket(hash int, numBuckets int) int {
	// In Go, -5 % 4 evaluates to -1
	idx := hash % numBuckets
	buckets := make([]int, numBuckets)
	return buckets[idx]
}

func main() {
	fmt.Println(getHashBucket(-5, 4))
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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package main import "fmt" func getHashBucket(hash int, numBuckets int) int { // In Go, -5 % 4 evaluates to -1 idx := hash % numBuckets buckets := make([]int, numBuckets) return buckets[idx] } func main() { fmt.Println(getHashBucket(-5, 4)) }

Negative modulo index out of range in hash bucket

What it should do

What happens instead

More logic errors to practise

Seen this error in your own code?

Negative modulo index out of range in hash bucket

What it should do

What happens instead

More logic errors to practise

Seen this error in your own code?