day 20, unit tests to debug == gold

2022/day20/main.go

@@ -0,0 +1,165 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+const part2DecryptionKey = 811589153
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := mixList(input, 1, 1)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := mixList(input, 811589153, 10)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func mixList(input string, decryptionKey, mixes int) int {
+	zeroNode, originalOrder := parseInput(input)
+
+	for i := 0; i < len(originalOrder); i++ {
+		originalOrder[i].val *= decryptionKey
+	}
+
+	for i := 0; i < mixes; i++ {
+		for _, node := range originalOrder {
+			node.move(len(originalOrder))
+		}
+	}
+
+	// sum 3 vals from  value zero, 1000th, 2000th, 3000th away
+
+	return getNodeXStepsAway(zeroNode, 1000, len(originalOrder)).val +
+		getNodeXStepsAway(zeroNode, 2000, len(originalOrder)).val +
+		getNodeXStepsAway(zeroNode, 3000, len(originalOrder)).val
+}
+
+func getNodeXStepsAway(node *llNode, steps int, listLength int) *llNode {
+	if steps < 0 {
+		panic("negative steps")
+	}
+
+	iter := node
+	for steps > 0 {
+		iter = iter.next
+		steps--
+	}
+	return iter
+}
+
+type llNode struct {
+	val        int
+	prev, next *llNode
+}
+
+func (n *llNode) move(totalLength int) {
+	steps := n.val
+	// fmt.Println("before steps", steps, "total", totalLength)
+	steps %= totalLength - 1
+
+	if steps == 0 {
+		// fmt.Println("zero steps")
+		return
+	}
+
+	// find slot to fit into
+
+	if steps < 0 {
+		steps += (totalLength - 1)
+	}
+	// fmt.Println("modded steps", steps)
+
+	oldPrev, oldNext := n.prev, n.next
+	oldPrev.next = oldNext
+	oldNext.prev = oldPrev
+
+	iter := n
+	for steps > 0 {
+		// fmt.Println("steps left", steps, "iter", iter)
+		iter = iter.next
+		if iter == n {
+			panic("repeat")
+		}
+		steps--
+	}
+
+	nextPrev, nextNext := iter, iter.next
+	// fmt.Println("nextPrev & nextNext", nextPrev, nextNext)
+	nextPrev.next = n
+	n.prev = nextPrev
+	nextNext.prev = n
+	n.next = nextNext
+}
+
+func parseInput(input string) (zeroNode *llNode, originalOrder []*llNode) {
+	nums := []int{}
+	for _, line := range strings.Split(input, "\n") {
+		nums = append(nums, cast.ToInt(line))
+	}
+
+	var head, iter *llNode
+	for _, n := range nums {
+		node := &llNode{
+			val:  n,
+			prev: iter,
+		}
+		if head == nil {
+			head = node
+			iter = node
+		} else {
+			iter.next = node
+			iter = iter.next
+		}
+
+		if iter.val == 0 {
+			zeroNode = iter
+		}
+		originalOrder = append(originalOrder, node)
+	}
+
+	head.prev = iter
+	iter.next = head
+
+	return zeroNode, originalOrder
+}
+
+// for debugging
+func listToString(head *llNode, listLength int) string {
+	var sb strings.Builder
+	for listLength > 0 {
+		sb.WriteString(cast.ToString(head.val) + ",")
+		head = head.next
+		listLength--
+	}
+	return sb.String()
+}
+
+func printList(head *llNode, listLength int) {
+	fmt.Println(listToString(head, listLength))
+}