AoC Day 8, Parts 1 and 2 (Solved)

2023/08/code.go

@@ -0,0 +1,121 @@
+package main
+
+import (
+	"regexp"
+	"strings"
+
+	"github.com/jpillora/puzzler/harness/aoc"
+)
+
+func main() {
+	aoc.Harness(run)
+}
+
+type Node struct {
+	Name  string
+	Left  string
+	Right string
+}
+
+func getLcm(a int, b int) int {
+	return (a * b) / getGcd(a, b)
+}
+
+func getGcd(a int, b int) int {
+	g := 0
+	for i := 1; i <= a && i <= b; i++ {
+		if a%i == 0 && b%i == 0 {
+			g = i
+		}
+	}
+	return g
+}
+
+// on code change, run will be executed 4 times:
+// 1. with: false (part1), and example input
+// 2. with: true (part2), and example input
+// 3. with: false (part1), and user input
+// 4. with: true (part2), and user input
+// the return value of each run is printed to stdout
+func run(part2 bool, input string) any {
+	nodeMap := make(map[string]*Node)
+
+	lines := strings.Split(input, "\n")
+	instructions := lines[0]
+
+	nodeRegex := regexp.MustCompile(`(?P<Name>[A-Z]+) = \((?P<Left>[A-Z]+), (?P<Right>[A-Z]+)\)`)
+	for _, line := range lines[1:] {
+		if line == "" {
+			continue
+		}
+
+		matches := nodeRegex.FindStringSubmatch(line)
+
+		name := matches[1]
+		left := matches[2]
+		right := matches[3]
+
+		thisNode := Node{name, left, right}
+		nodeMap[name] = &thisNode
+	}
+
+	// when you're ready to do part 2, remove this "not implemented" block
+	if part2 {
+		ghostNodes := make([]*Node, 0)
+		for nodeName, node := range nodeMap {
+			if rune(nodeName[2]) == 'A' {
+				// Start node
+				ghostNodes = append(ghostNodes, node)
+			}
+		}
+
+		// Find the minimal... something?
+		minSteps := make([]int, 0)
+		for _, ghostNode := range ghostNodes {
+			node := ghostNode
+			steps := 0
+
+			for rune(node.Name[2]) != 'Z' {
+				instr := rune(instructions[steps%len(instructions)])
+
+				if instr == 'L' {
+					// Left
+					node = nodeMap[node.Left]
+				} else {
+					// Right
+					node = nodeMap[node.Right]
+				}
+
+				steps += 1
+			}
+
+			minSteps = append(minSteps, steps)
+		}
+
+		lcm := 1
+		for _, st := range minSteps {
+			lcm = getLcm(lcm, st)
+		}
+
+		return lcm
+	}
+	// solve part 1 here
+
+	node := nodeMap["AAA"]
+	totalSteps := 0
+	for node.Name != "ZZZ" {
+		instr := rune(instructions[totalSteps%len(instructions)])
+
+		if instr == 'L' {
+			// Left
+			node = nodeMap[node.Left]
+		} else {
+			// Right
+			node = nodeMap[node.Right]
+		}
+
+		totalSteps += 1
+	}
+
+	return totalSteps
+}