day-8

day-8/go.mod

@@ -0,0 +1,3 @@
+module github.com/onyx-and-iris/aoc2023/day-8
+
+go 1.20

day-8/one.go

@@ -0,0 +1,28 @@
+package main
+
+const (
+	LEFT = iota // 0
+	RIGHT
+)
+
+var directions string
+var steps = map[string][]string{}
+
+// one returns the number of steps to reach 'ZZZ'
+func one(lines []string) int {
+	parselines(lines)
+
+	num := 0
+	for i, step := 0, "AAA"; step != "ZZZ"; i, num = i+1, num+1 {
+		if i == len(directions) {
+			i = 0
+		}
+		if directions[i] == 'L' {
+			step = steps[step][LEFT]
+		} else {
+			step = steps[step][RIGHT]
+		}
+	}
+
+	return num
+}

day-8/run.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+INPUT="input.txt"
+
+cat $INPUT | go run .

day-8/solution.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func init() {
+	log.SetLevel(log.InfoLevel)
+}
+
+func main() {
+	lines := readlines()
+
+	ans := one(lines)
+	fmt.Printf("solution one: %d\n", ans)
+
+	ans = two(lines)
+	fmt.Printf("solution two: %d\n", ans)
+}

day-8/two.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"strings"
+)
+
+// GCF returns the greatest common factor of two numbers
+func GCF(a, b int) int {
+	for b != 0 {
+		t := b
+		b = a % b
+		a = t
+	}
+	return a
+}
+
+// LCM returns least common multiple of a set a numbers
+func LCM(a, b int, integers ...int) int {
+	result := a * b / GCF(a, b)
+
+	for i := 0; i < len(integers); i++ {
+		result = LCM(result, integers[i])
+	}
+
+	return result
+}
+
+// two returns minimum steps required until all routes end with '*Z'
+func two(lines []string) int {
+	parselines(lines)
+
+	startpoints := make([]string, 0)
+	for k := range steps {
+		if strings.HasSuffix(k, "A") {
+			startpoints = append(startpoints, k)
+		}
+	}
+
+	nums := []int{}
+	for _, step := range startpoints {
+		num := 0
+		for i := 0; !strings.HasSuffix(step, "Z"); i, num = i+1, num+1 {
+			if i == len(directions) {
+				i = 0
+			}
+			if directions[i] == 'L' {
+				step = steps[step][LEFT]
+			} else {
+				step = steps[step][RIGHT]
+			}
+		}
+		nums = append(nums, num)
+	}
+
+	lcm := 0
+	lcm = LCM(nums[0], nums[1], nums[2:]...)
+
+	return lcm
+}

day-8/util.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"bufio"
+	"log"
+	"os"
+	"regexp"
+)
+
+// readlines reads lines from stdin.
+// returns input as an array of strings
+func readlines() []string {
+	lines := []string{}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+
+	if err := scanner.Err(); err != nil {
+		log.Fatal(err)
+	}
+
+	return lines
+}
+
+var r = regexp.MustCompile(`(?P<identifier>[A-Z0-9]{3}) = \((?P<entry>[A-Z0-9]{3}), (?P<exit>[A-Z0-9]{3})\)`)
+
+func parselines(lines []string) {
+	directions = lines[0]
+
+	steps = make(map[string][]string, len(lines[2:]))
+	for _, line := range lines[2:] {
+		m := r.FindStringSubmatch(line)
+		if len(m) > 0 {
+			steps[m[1]] = []string{m[2], m[3]}
+		}
+	}
+}