codewars/go/kyu5/maximum_subarray_sum/k.go

package kata

func isDegeneratePositive(numbers []int) bool {
	for _, n := range numbers {
		if n < 0 {
			return false
		}
	}
	return true
}

func isDegenerateNegative(numbers []int) bool {
	for _, n := range numbers {
		if n > 0 {
			return false
		}
	}
	return true
}

func sum(s []int) int {
	res := 0
	for _, n := range s {
		res += n
	}
	return res
}

func MaximumSubarraySum(numbers []int) int {
	// Covers the empty case as well.
	if isDegeneratePositive(numbers) {
		return sum(numbers)
	}
	// Would cover the empty case as well, but it was handled above.
	if isDegenerateNegative(numbers) {
		return 0
	}

	max := 0
	for i := 0; i < len(numbers); i++ {
		for j := i; j <= len(numbers); j++ {
			sliced := numbers[i:j]
			candidate := sum(sliced)
			if candidate > max {
				max = candidate
			}
		}
	}
	return max
}