2023 Day 8 Complete

2023/day08/main.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	part1(inp)
+	fmt.Println()
+	part2(inp)
+}
+
+type node struct {
+	left, right string
+}
+
+func build(input []string) (string, map[string]node) {
+	inst := input[0]
+	input = input[2:]
+	m := make(map[string]node)
+	for i := range input {
+		var name, l, r string
+		fmt.Sscanf(input[i], "%s = (%3s, %3s)", &name, &l, &r)
+		m[name] = node{left: l, right: r}
+	}
+	return inst, m
+}
+
+func part1(input []string) {
+	inst, m := build(input)
+	curr := "AAA"
+	instIdx := 0
+	for curr != "ZZZ" {
+		switch inst[instIdx%len(inst)] {
+		case 'L':
+			curr = m[curr].left
+		case 'R':
+			curr = m[curr].right
+		}
+		instIdx++
+	}
+	fmt.Println("# Part 1")
+	fmt.Println(instIdx)
+}
+
+func part2(input []string) {
+	inst, m := build(input)
+	// Find all starting nodes
+	var starts []string
+	for k := range m {
+		if k[2] == 'A' {
+			starts = append(starts, k)
+		}
+	}
+	var dists []int
+	// Find the distances from 'starts' to the end nodes
+	for _, v := range starts {
+		cnt := 0
+		distMap := make(map[string]int)
+		// find the path to a 'Z'
+		for {
+			if v[2] == 'Z' {
+				// Found it
+				key := fmt.Sprintf("%s-%d", v, cnt%len(inst))
+				if distMap[key] == 1 {
+					break
+				}
+				distMap[key] = 1
+				dists = append(dists, cnt)
+			}
+			switch inst[cnt%len(inst)] {
+			case 'L':
+				v = m[v].left
+			case 'R':
+				v = m[v].right
+			}
+			cnt++
+		}
+	}
+
+	cnt := 1
+	for _, n := range dists {
+		cnt = h.Lcm(cnt, n)
+	}
+
+	fmt.Println("# Part 2")
+	fmt.Println(cnt)
+}