快速排序

func quickSort(arr []int) []int {
        return _quickSort(arr, 0, len(arr)-1)
}

func _quickSort(arr []int, left, right int) []int {
        if left < right {
                partitionIndex := partition(arr, left, right)
                _quickSort(arr, left, partitionIndex-1)
                _quickSort(arr, partitionIndex+1, right)
        }
        return arr
}

func partition(arr []int, left, right int) int {
        pivot := left
        index := pivot + 1

        for i := index; i <= right; i++ {
                if arr[i] < arr[pivot] {
                        swap(arr, i, index)
                        index += 1
                }
        }
        swap(arr, pivot, index-1)
        return index - 1
}

func swap(arr []int, i, j int) {
        arr[i], arr[j] = arr[j], arr[i]
}