goLogic errorHard

Shallow copy of 2D slice mutates original

Time: 0:00

BugFind the bug and fix the code

What it should do

Clone a 2D integer slice and mutate first cell without modifying original. Example: cloneAndMutateGrid(99) -> [0, 99]

What happens instead

Original grid cell is mutated because inner slices were shared

package main

import "fmt"

func cloneAndMutateGrid(newVal int) []int {
	original := [][]int{{0, 1}, {2, 3}}
	// Shallow copy copies slice headers, pointing to same underlying row arrays
	clone := make([][]int, len(original))
	copy(clone, original)
	clone[0][0] = newVal
	return []int{original[0][0], clone[0][0]}
}

func main() {
	fmt.Println(cloneAndMutateGrid(99))
}

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.

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package main import "fmt" func cloneAndMutateGrid(newVal int) []int { original := [][]int{{0, 1}, {2, 3}} // Shallow copy copies slice headers, pointing to same underlying row arrays clone := make([][]int, len(original)) copy(clone, original) clone[0][0] = newVal return []int{original[0][0], clone[0][0]} } func main() { fmt.Println(cloneAndMutateGrid(99)) }

Shallow copy of 2D slice mutates original

What it should do

What happens instead

More logic errors to practise

Shallow copy of 2D slice mutates original

What it should do

What happens instead

More logic errors to practise