Sorting algorithms in Go (Selection sort, Insertion sort, Bubble sort, Merge sort, Quick sort)

sorting.go

package main

import (
	"fmt"
	"math/rand"
	"time"
)

func main() {

	rand.Seed(time.Now().UnixNano())

	a := make([]int, rand.Intn(20))
	for i := range a {
		rand.Int()
		a[i] = rand.Intn(999) - rand.Intn(555)
	}
	a = append(a, 0)

	fmt.Println(SelectionSort(a))
	fmt.Println(InsertionSort(a))
	fmt.Println(BubbleSort(a))

	fmt.Println(MergeSort(a))
	fmt.Println(QuickSort(a))
}

// selectionsort
func SelectionSort(arr []int) []int {

	for i := 0; i < len(arr)-1; i++ {
		for j := i + 1; j < len(arr); j++ {
			if arr[j] < arr[i] {
				arr[i], arr[j] = arr[j], arr[i]
			}
		}
	}

	return arr
}

// insertionsort
func InsertionSort(arr []int) []int {

	for i := 1; i < len(arr); i++ {
		current := arr[i]
		j := i - 1
		for j >= 0 && arr[j] > current {
			arr[j], arr[j+1] = arr[j+1], arr[j]
			j--
		}
	}

	return arr
}

// bubblesort
func BubbleSort(arr []int) []int {

	for i := 1; i < len(arr); i++ {
		for j := 0; j < len(arr)-i; j++ {
			if arr[j] > arr[j+1] {
				arr[j], arr[j+1] = arr[j+1], arr[j]
			}
		}
	}

	return arr
}

// MergeSort
func MergeSort(arr []int) []int {
	l := len(arr)
	if l < 2 {
		return arr
	}

	return merge(MergeSort(arr[:l/2]), MergeSort(arr[l/2:]))
}

func merge(left, right []int) []int {
	i, j := 0, 0
	res := []int{}

	for i < len(left) && j < len(right) {
		if left[i] < right[j] {
			res = append(res, left[i])
			i++
		} else {
			res = append(res, right[j])
			j++
		}
	}

	for i < len(left) {
		res = append(res, left[i])
		i++
	}
	for j < len(right) {
		res = append(res, right[j])
		j++
	}

	return res
}

// QuickSort
func QuickSort(arr []int) []int {
	quickSortHelper(arr, 0, len(arr)-1)
	return arr
}

func quickSortHelper(arr []int, strIdx, endIdx int) {
	if strIdx >= endIdx {
		return
	}

	pivot := strIdx
	left := strIdx + 1
	right := endIdx

	//partition algorithm
	for left <= right {
		if arr[left] > arr[pivot] && arr[right] < arr[pivot] {
			arr[left], arr[right] = arr[right], arr[left]
			left++
			right--
		}
		if arr[left] <= arr[pivot] {
			left++
		} else if arr[right] >= arr[pivot] {
			right--
		}
	}
	arr[right], arr[pivot] = arr[pivot], arr[right]

	quickSortHelper(arr, strIdx, right-1)
	quickSortHelper(arr, right+1, endIdx)
}