day08

2023/go/day08/day08.go

@@ -0,0 +1,99 @@
+package day08
+
+import (
+	 _ "fmt"
+	_ "adventofcode2023/utils"
+	"regexp"
+	"strings"
+	"math"
+)
+
+type Node struct {
+	left string
+	right string
+}
+
+type Network map[string]Node
+
+func Part1(input string) int {
+	instructions, network := parseInput(input)
+	return getSteps("AAA", instructions, network, true)
+}
+
+func Part2(input string) int {
+	instructions, nexts, network := parseInput2(input)
+	ans := 1
+	for _, next := range nexts {
+		ans = lcm(ans, getSteps(next, instructions, network, false))
+	}
+	return ans
+}
+
+// gcd calculates the greatest common divisor using Euclid's algorithm
+func gcd(a, b int) int {
+	for b != 0 {
+		a, b = b, a%b
+	}
+	return a
+}
+
+// lcm calculates the least common multiple using the formula: LCM(a, b) = |a * b| / GCD(a, b)
+func lcm(a, b int) int {
+	if a == 0 || b == 0 {
+		return 0
+	}
+	return int(math.Abs(float64(a*b)) / float64(gcd(a, b)))
+}
+
+func parseInput(input string) ([]rune, Network) {
+	network := make(Network)
+	lines := strings.Split(input, "\n")
+	instructions := []rune(lines[0])
+	re := regexp.MustCompile(`(\w+) = \((\w+), (\w+)\)`)
+	
+	for _, line := range lines[2:] {
+		matches := re.FindAllStringSubmatch(line, -1)
+		network[matches[0][1]] = Node{matches[0][2], matches[0][3]}
+	}
+	return instructions, network
+}
+
+func parseInput2(input string) ([]rune, []string, Network) {
+	network := make(Network)
+	lines := strings.Split(input, "\n")
+	start := []string{}
+	instructions := []rune(lines[0])
+	re := regexp.MustCompile(`(\w+) = \((\w+), (\w+)\)`)
+	
+	for _, line := range lines[2:] {
+		matches := re.FindAllStringSubmatch(line, -1)
+		network[matches[0][1]] = Node{matches[0][2], matches[0][3]}
+		if matches[0][1][2] == 'A' {
+			start = append(start, matches[0][1])
+		}
+	}
+	return instructions, start, network
+}
+
+func getSteps(next string, instructions []rune, network Network, partOne bool) int{
+	steps := 0
+	for {
+		for _, ins := range instructions {
+			steps++
+			if ins == 'L' {
+				next = network[next].left
+			} else {
+				next = network[next].right
+			}
+			if partOne {
+				if next == "ZZZ" {
+					return steps
+				}
+			} else {
+				if next[2] == 'Z' {
+					return steps
+				}
+			}
+		}
+	}
+}