Implemtation of counting sort in go

counting_sort.go

func countingSort(slice []Customer) []Customer {
	// slice `sortedSlice` is created to store the sorted values
	sortedSlice := make([]Customer, len(slice))
	// slice `countSlice` is created to store the count of each value (line 32).
	countSlice := make([]int, len(slice))
	
	// `countSlice` is populated by iterating over the input `slice` and incrementing the count of each `Customer`'s `numPurchases`
	for _, customer := range slice {
		countSlice[customer.numPurchases]++
	}

	// `countSlice` is then updated to show cumulative counts
	// This will help in determining the correct position of each element in the sorted output.
	for i := 1; i < len(countSlice); i++ {
		countSlice[i] += countSlice[i-1]
	}
	
	// original `slice` is iterated in reverse order.
	// For each `Customer`, its `numPurchases` is used to find the correct position in the `sortedSlice`
	// the `Customer` is placed in the `sortedSlice`,
	// and the count in `countSlice` is decremented
	for i := len(slice) - 1; i >= 0; i-- {
		index := countSlice[slice[i].numPurchases] - 1
		sortedSlice[index] = slice[i]
		countSlice[slice[i].numPurchases]--
	}
	
	// return the sorted slice
	return sortedSlice
}