From 228a6853e2c25287287cfb3596229cdbf784f150 Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Wed, 16 Dec 2020 22:34:17 -0500
Subject: [PATCH] 2017-day17: brute force

---
 2017/day17/main.go      | 66 +++++++++++++++++++++++++++++++++++++++++
 2017/day17/main_test.go | 31 +++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 2017/day17/main.go
 create mode 100644 2017/day17/main_test.go

diff --git a/2017/day17/main.go b/2017/day17/main.go
new file mode 100644
index 0000000..c2d6c59
--- /dev/null
+++ b/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
+}
diff --git a/2017/day17/main_test.go b/2017/day17/main_test.go
new file mode 100644
index 0000000..2f2fc76
--- /dev/null
+++ b/2017/day17/main_test.go
@@ -0,0 +1,31 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_spinlock(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"example_part1", "3", 1, 638},
+		{"actual_part1", util.ReadFile("input.txt"), 1, 1547},
+		{"actual_part2", util.ReadFile("input.txt"), 2, 31154878},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Logf("Running %s", tt.name)
+			if tt.name == "actual_part2" {
+				t.Log("This one could take a while, it has 50 million steps to run")
+			}
+			if got := spinlock(tt.input, tt.part); got != tt.want {
+				t.Errorf("spinlock() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}