day03.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"path/filepath"
	"strings"
)

type Coordinates struct {
	x, y int
}

// Read the input file.
func getInput() []string {
	filepath, err := filepath.Abs("2020/inputs/day03.txt")
	if err != nil {
		log.Fatal(err)
	}

	inputVal, err := ioutil.ReadFile(filepath)
	if err != nil {
		log.Fatal(err)
	}

	return strings.Split(string(inputVal), "\n")
}

// Traverse the input at a slope of 3 right, 1 down and
// count the number of "trees"
func partOne(inputVal []string) int {
	position := Coordinates{0, 0}
	mapWidth := len(inputVal[0])
	nTrees := 0
	slope := []int{3, 1}

	for i, element := range inputVal {
		position.x = slope[0] * i
		position.y = slope[1] * i
		offset := (position.x / mapWidth) * mapWidth
		adjustedPosition := Coordinates{position.x - offset, position.y}
		if string(element[adjustedPosition.x]) == "#" {
			nTrees++
		}
	}

	return nTrees
}

// Traverse the input for a variety of slopes and multiple the results.
func partTwo(inputVal []string) int {
	position := Coordinates{0, 0}
	mapWidth := len(inputVal[0])
	var results []int
	slopes := [][]int{
		{1, 1},
		{3, 1},
		{5, 1},
		{7, 1},
		{1, 2},
	}

	for _, slope := range slopes {
		nTrees := 0
		for i := 0; i < len(inputVal); i += slope[1] {
			element := inputVal[i]
			position.x = slope[0] * i
			position.y = slope[1] * i
			offset := (position.x / mapWidth) * mapWidth
			adjustedPosition := Coordinates{position.x - offset, position.y}
			fmt.Println(i, offset, position, adjustedPosition)
			if string(element[adjustedPosition.x]) == "#" {
				nTrees++
			}
		}
		results = append(results, nTrees)
	}

	// Multiply the results together
	answer := 1

	for _, result := range results {
		answer *= result
	}

	return answer
}

func main() {
	inputVal := getInput()
	partOneAnswer := partOne(inputVal)
	partTwoAnswer := partTwo(inputVal)
	fmt.Printf("PartOne - Number of Trees: %d\n", partOneAnswer)
	fmt.Printf("PartTwo - Number of Trees Multiplied: %d", partTwoAnswer)
}