From eb24a4e54813276a41c8b168d224b4907f6b5f80 Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Sun, 20 Dec 2020 19:04:39 -0500
Subject: [PATCH] 2020-day23: ugh manually optimizing assembly

---
 2017/day23/main.go      | 122 ++++++++++++++++++++++++++++++++++++++++
 2017/day23/main_test.go |  41 ++++++++++++++
 2 files changed, 163 insertions(+)
 create mode 100644 2017/day23/main.go
 create mode 100644 2017/day23/main_test.go

diff --git a/2017/day23/main.go b/2017/day23/main.go
new file mode 100644
index 0000000..a9ab286
--- /dev/null
+++ b/2017/day23/main.go
@@ -0,0 +1,122 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"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)
+
+	var ans int
+	if part == 1 {
+		ans = part1(util.ReadFile("./input.txt"))
+	} else {
+		ans = part2(util.ReadFile("./input.txt"))
+	}
+	fmt.Println("Output:", ans)
+}
+
+// literal implementation for part 1
+func part1(input string) int {
+	comp := newComputerFromInput(input)
+	// prime until it gets a valid receive command, then return last outputted num
+	return comp.countMulsRun()
+}
+
+// referenced this heavily: https://www.reddit.com/r/adventofcode/comments/7lms6p/2017_day_23_solutions/drnh5sx?utm_source=share&utm_medium=web2x&context=3
+func part2(input string) int {
+	b := 81
+	c := 81
+
+	b = b*100 + 100000
+	c = b + 17000
+	var h int
+	for {
+		f := 1
+		// effectively a prime number checker.
+		for d := 2; d*d <= b; d++ {
+			if b%d == 0 {
+				f = 0
+				break
+			}
+		}
+
+		if f == 0 {
+			h++
+		}
+		if b == c {
+			break
+		}
+		b += 17
+	}
+
+	return h
+}
+
+type computer struct {
+	instructions [][]string
+	pointer      int
+	registers    map[string]int
+	output       []int
+}
+
+func newComputerFromInput(input string) *computer {
+	comp := &computer{registers: map[string]int{}}
+	for _, line := range strings.Split(input, "\n") {
+		comp.instructions = append(comp.instructions, strings.Split(line, " "))
+	}
+
+	return comp
+}
+
+func (c *computer) countMulsRun() (mulsRun int) {
+	for c.pointer < len(c.instructions) {
+		inst := c.instructions[c.pointer]
+		valX := inst[1]
+		var valFromY int
+		if val, err := strconv.Atoi(inst[2]); err != nil {
+			// if there is an error parsing to an integer, value at index 1 is a register
+			valFromY = c.registers[inst[2]]
+		} else {
+			valFromY = val
+		}
+
+		switch inst[0] {
+		case "set":
+			c.registers[valX] = valFromY
+			c.pointer++
+		case "sub":
+			c.registers[valX] -= valFromY
+			c.pointer++
+		case "mul":
+			c.registers[valX] *= valFromY
+			c.pointer++
+			mulsRun++
+		case "jnz":
+			var parsedX int
+			if num, err := strconv.Atoi(valX); err != nil {
+				// err converting, not a number
+				parsedX = c.registers[valX]
+			} else {
+				// no error then a number was parsed
+				parsedX = num
+			}
+			if parsedX != 0 {
+				c.pointer += valFromY
+			} else {
+				c.pointer++
+			}
+		default:
+			panic("unhandled operator " + inst[0])
+		}
+	}
+	return mulsRun
+}
diff --git a/2017/day23/main_test.go b/2017/day23/main_test.go
new file mode 100644
index 0000000..edaa849
--- /dev/null
+++ b/2017/day23/main_test.go
@@ -0,0 +1,41 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 6241},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_part2(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 909},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}