https://adventofcode.com/2020/day/3

tree_encounter.go

package main

import (
	"io/ioutil"
	"strings"
)

func main() {

	bytes, _ := ioutil.ReadFile("./input.txt")
	input := strings.TrimRight(string(bytes), "\n")

	pattern := make([][]string, 0, 0)
	for i, row := range strings.Split(input, "\n") {
		pattern = append(pattern, make([]string, 0, 0))
		for _, char := range row {
			pattern[i] = append(pattern[i], string(char))
		}
	}

	encounter := 0
	x := 0

	for y := 0; y < len(pattern); y++ {
		if pattern[y][x] == "#" {
			encounter++
		}
		x += 3
		if x >= len(pattern[y]) {
			x -= len(pattern[y])
		}
	}

	println(encounter)
}

tree_encounter2.go

package main

import (
	"io/ioutil"
	"strings"
)

func main() {

	bytes, _ := ioutil.ReadFile("./input.txt")
	input := strings.TrimRight(string(bytes), "\n")

	pattern := make([][]string, 0, 0)
	for i, row := range strings.Split(input, "\n") {
		pattern = append(pattern, make([]string, 0, 0))
		for _, char := range row {
			pattern[i] = append(pattern[i], string(char))
		}
	}

	slopes := [][]int{
		{1, 1},
		{3, 1},
		{5, 1},
		{7, 1},
		{1, 2},
	}
	r := 1
	for _, slope := range slopes {
		r *= count(pattern, slope[0], slope[1])
	}
	println(r)
}

func count(pattern [][]string, xp int, yp int) int {
	encounter := 0
	x := 0

	for y := 0; y < len(pattern); y += yp {
		if pattern[y][x] == "#" {
			encounter++
		}
		x += xp
		if x >= len(pattern[y]) {
			x -= len(pattern[y])
		}
	}

	return encounter
}