Max interval sum in go

max_interval_sum.go

package main

import "fmt"
import "errors"

type sumTracker []int

func (self sumTracker) add(i, j, amount int) error {
	if i > j {
		return errors.New("range order")
	}
	if i < 0 || j >= len(self) {
		return errors.New("bounds")
	}
	if amount < 0 {
		return errors.New("amount")
	}
	self[j] += amount
	if i > 0 {
		self[i-1] -= amount
	}
	return nil
}

func (self sumTracker) totals() (totals []int) {
	totals = make([]int, len(self))
	delta := 0
	for i := len(self) - 1; i > 0; i-- {
		delta += self[i]
		totals[i] = delta
	}
	return
}

func maxPosValue(totals []int) (maxPos int, maxAmount int) {
	for i, amount := range totals {
		if amount > maxAmount {
			maxPos = i
			maxAmount = amount
		}
	}
	return
}

func main() {
	tracker := make(sumTracker, 10)
	tracker.add(0, 9, 1)
	tracker.add(0, 5, 3)
	tracker.add(4, 7, 2)
	tracker.add(8, 8, 4)
	fmt.Printf("deltas: %+v\n", tracker)
	totals := tracker.totals()
	fmt.Printf("totals: %v\n", totals)
	maxPos, maxValue := maxPosValue(totals)
	fmt.Printf("max: %v at pos %v\n", maxPos, maxValue)
}