learn_golang/learn_go_with_tests/arrays/sum.go

package arrays

func Sum(a []int) int {
	sum := 0

	//aternatively
	// for i := 0; i < 5; i++ {
	// 	sum += a[i]
	// }

	// OR

	// for i := range a {
	// 	sum += a[i]
	// }

	// OR

	for _, v := range a {
		sum += v
	}
	return sum
}

// The ... in the method signature means it's  variadic function
// meaning it takes a variable number of arguments

// SumAll
func SumAll(numbersToSum ...[]int) []int {
	// lengthOfNumbers := len(numbersToSum)

	//There's a new way to create a slice. make allows you to create a slice with a starting capacity of the len of the numbersToSum we need to work through.
	// sums := make([]int, lengthOfNumbers)

	// for i, numbers := range numbersToSum {
	// 	sums[i] = Sum(numbers)
	// }

	// Using the append method you do not have to worry about capacity and index errors
	// append will create a new slice with greater capacity and the new value added to it.
	// The is a different between len() and capacity() capacity is the allocated size, and there
	// is an algorithm used by append to determine when it needs to change.
	var sums []int

	for _, numbers := range numbersToSum {
		sums = append(sums, Sum(numbers))
	}

	return sums
}

func SumAllTails(numbersToSum ...[]int) []int {
	var sums []int

	for _, numbers := range numbersToSum {
		if len(numbers) == 0 {
			sums = append(sums, 0)
		} else {
			tails := numbers[1:]
			sums = append(sums, Sum(tails))
		}
	}

	return sums
}