2017-day17: brute force

2017/day17/main.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+
+	"github.com/alexchao26/advent-of-code-go/mathutil"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := spinlock(util.ReadFile("./input.txt"), part)
+	util.CopyToClipboard(fmt.Sprintf("%v", ans))
+	fmt.Println("Output:", ans)
+}
+
+type llNode struct {
+	value int
+	next  *llNode
+}
+
+func spinlock(input string, part int) int {
+	steps := mathutil.StrToInt(input)
+
+	lastNumToAdd := 2017
+	if part == 2 {
+		lastNumToAdd = 50000000
+	}
+
+	current := &llNode{value: 0}
+	current.next = current
+	for i := 1; i <= lastNumToAdd; i++ {
+		for j := 0; j < steps; j++ {
+			current = current.next
+		}
+
+		saveNext := current.next
+		current.next = &llNode{
+			value: i,
+			next:  saveNext,
+		}
+		current = current.next
+
+		// progress log for part 2 brute force...
+		if i%1000000 == 0 {
+			log.Println(i, "steps done")
+		}
+	}
+
+	// iterate to the node to find, then return the value of the next node
+	valueToFind := 2017
+	if part == 2 {
+		valueToFind = 0
+	}
+	for current.value != valueToFind {
+		current = current.next
+	}
+
+	return current.next.value
+}