adventofcode2023/day09.go

package main

import (
	"bufio"
	"fmt"
	"io"
)

func allzeros(ints []int) bool {
	for i := range ints {
		if ints[i] != 0 {
			return false
		}
	}
	return true
}

func nextOasis(previous int, start []int) int {
	if allzeros(start) {
		return 0
	}

	length := len(start) - 1
	levelBelow := make([]int, 0, length)
	for i := 0; i < length; i++ {
		levelBelow = append(levelBelow, start[i+1]-start[i])
	}

	current := start[length]
	return current + nextOasis(current, levelBelow)
}

func previousOasis(previous int, start []int) int {
	return 0
}

type day09 struct{}

func (d day09) solve1(r io.Reader) string {
	scanner := bufio.NewScanner(r)
	total := 0

	for scanner.Scan() {
		total += nextOasis(0, scanints(scanner.Text()))
	}
	return fmt.Sprintf("%d", total)
}

func (d day09) solve2(r io.Reader) string {
	scanner := bufio.NewScanner(r)
	total := 0

	for scanner.Scan() {
		ints := scanints(scanner.Text())
		reverseSlice(ints)
		total += nextOasis(0, ints)
	}
	return fmt.Sprintf("%d", total)
}