trouble using pointer in Golang

Question

I am new to golang, here I am using BubleSort and InsertionSort and generating a rando slice for the functions. Can I use pointers some how to hand both functions the unsorted slice? because when I run the program the first function sorts the slice and the the second function uses that sorted slice. I know there are different ways to give both functions the unsorted slice, but I want to see how can I use pointers to do this. Thank you.

package main

import (
"fmt"

"math/rand"

"time"
)

func main() {
slice := generateSlice(4)
fmt.Println(BubleSort(slice))
fmt.Println(InsertionSort(slice))
}

func generateSlice(size int) []int {
slice := make([]int, size, size)
rand.Seed(time.Now().UnixNano())
for i := 0; i < size; i++ {
    slice[i] = rand.Intn(10)
}
return slice
}

func BubleSort(slice []int) []int {
fmt.Println("unsorted Buble", slice)
for i := 1; i <= len(slice); {
    for j := 0; j < len(slice)-i; {
        if slice[j] > slice[j+1] {
            slice[j], slice[j+1] = slice[j+1], slice[j]
        }
        j++
    }
    i++
}
return slice
}

func InsertionSort(slice []int) []int {
fmt.Println("unsorted Insertion", slice)
for i := 1; i <= len(slice)-1; {
    // Check j and j-1 and swap the smaller number to left in each 
itteartion to reach the first 2 elements of the slice
    for j := i; j >= 1; {
        if slice[j] < slice[j-1] {
            slice[j], slice[j-1] = slice[j-1], slice[j]
        }
        j--
    }
    i++
}
return slice
}

David Budworth · Accepted Answer · 2017-11-05 15:38:25Z

Andy is correct

As an alternative, you can copy the slice before sorting it, as in here (on Play):

package main

import (
    "fmt"

    "math/rand"

    "time"
)

func main() {
    slice := generateSlice(4)
    fmt.Println(BubleSort(copySlice(slice)))
    fmt.Println(InsertionSort(copySlice(slice)))
}

func copySlice(src []int) []int {
    dest := make([]int, len(src))
    copy(dest, src)
    return dest
}
func generateSlice(size int) []int {
    slice := make([]int, size, size)
    rand.Seed(time.Now().UnixNano())
    for i := 0; i < size; i++ {
        slice[i] = rand.Intn(10)
    }
    return slice
}

func BubleSort(slice []int) []int {
    fmt.Println("unsorted Buble", slice)
    for i := 1; i <= len(slice); {
        for j := 0; j < len(slice)-i; {
            if slice[j] > slice[j+1] {
                slice[j], slice[j+1] = slice[j+1], slice[j]
            }
            j++
        }
        i++
    }
    return slice
}

func InsertionSort(slice []int) []int {
    fmt.Println("unsorted Insertion", slice)
    for i := 1; i <= len(slice)-1; {
        // Check j and j-1 and swap the smaller number to left in each itteartion to reach the first 2 elements of the slice
        for j := i; j >= 1; {
            if slice[j] < slice[j-1] {
                slice[j], slice[j-1] = slice[j-1], slice[j]
            }
            j--
        }
        i++
    }
    return slice
}

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

I am learning Go as well. I think the fact that you are using slice is what causing the unwanted behaviour (when I run the program the first function sorts the slice and the the second function uses that sorted slice). As explained here:

A slice does not store any data, it just describes a section of an underlying array.

Changing the elements of a slice modifies the corresponding elements of its underlying array.

Other slices that share the same underlying array will see those changes.

I don't think passing pointer will produce different results as slices point to the same array. What you can do is maybe receive an array instead of slice?

Hope it helps! :)

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Nov 5, 2017 at 14:57

Andy Aldo

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