From 9b67f2728c0ff2533e56c937dd2866941b6c8fd2 Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Mon, 2 Dec 2019 19:20:52 +0100
Subject: [PATCH] Add solution for Day 2

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 day02.go        | 121 ++++++++++++++++++++++++++++++++++++++++++++++++
 day02_input.txt |   1 +
 day02_test.go   |  47 +++++++++++++++++++
 3 files changed, 169 insertions(+)
 create mode 100644 day02.go
 create mode 100644 day02_input.txt
 create mode 100644 day02_test.go

diff --git a/day02.go b/day02.go
new file mode 100644
index 0000000..3a67245
--- /dev/null
+++ b/day02.go
@@ -0,0 +1,121 @@
+package aoc2019
+
+import (
+	"io/ioutil"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+func parseDay02Intcode(code string) ([]int, error) {
+	parts := strings.Split(code, ",")
+
+	var out []int
+	for _, n := range parts {
+		v, err := strconv.Atoi(n)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, v)
+	}
+
+	return out, nil
+}
+
+func executeDay02Intcode(code []int) ([]int, error) {
+	var (
+		pos int
+		run = true
+	)
+
+	for run {
+		if pos >= len(code) {
+			return nil, errors.Errorf("Code position out of bounds: %d (len=%d)", pos, len(code))
+		}
+
+		switch code[pos] {
+		case 1:
+			// addition
+			p1, p2, pt := code[pos+1], code[pos+2], code[pos+3]
+			code[pt] = code[p1] + code[p2]
+
+		case 2:
+			// multiplication
+			p1, p2, pt := code[pos+1], code[pos+2], code[pos+3]
+			code[pt] = code[p1] * code[p2]
+
+		case 99:
+			// program finished
+			run = false
+
+		default:
+			return nil, errors.Errorf("Encountered invalid operation %d", code[pos])
+		}
+
+		pos += 4
+	}
+
+	return code, nil
+}
+
+func solveDay2Part1(inFile string) (int, error) {
+	raw, err := ioutil.ReadFile(inFile)
+	if err != nil {
+		return 0, errors.Wrap(err, "Unable to read input")
+	}
+
+	code, err := parseDay02Intcode(strings.TrimSpace(string(raw)))
+	if err != nil {
+		return 0, errors.Wrap(err, "Unable to parse Intcode")
+	}
+
+	// Modify data for "1202 program alarm"
+	code[1] = 12
+	code[2] = 2
+
+	// Execute Intcode
+	code, err = executeDay02Intcode(code)
+	if err != nil {
+		return 0, errors.Wrap(err, "Unable to execute Intcode")
+	}
+
+	return code[0], nil
+}
+
+func solveDay2Part2(inFile string) (int, error) {
+	raw, err := ioutil.ReadFile(inFile)
+	if err != nil {
+		return 0, errors.Wrap(err, "Unable to read input")
+	}
+
+	const expectedResult int = 19690720
+
+	for noun := 0; noun < 100; noun++ {
+		for verb := 0; verb < 100; verb++ {
+
+			// Re-initialize "memory"
+			code, err := parseDay02Intcode(strings.TrimSpace(string(raw)))
+			if err != nil {
+				return 0, errors.Wrap(err, "Unable to parse Intcode")
+			}
+
+			// Modify code
+			code[1] = noun
+			code[2] = verb
+
+			// Execute Intcode
+			code, err = executeDay02Intcode(code)
+			if err != nil {
+				return 0, errors.Wrap(err, "Unable to execute Intcode")
+			}
+
+			if code[0] == expectedResult {
+				return 100*noun + verb, nil
+			}
+
+		}
+	}
+
+	return 0, errors.New("No valid result was found")
+}
diff --git a/day02_input.txt b/day02_input.txt
new file mode 100644
index 0000000..e7533e2
--- /dev/null
+++ b/day02_input.txt
@@ -0,0 +1 @@
+1,0,0,3,1,1,2,3,1,3,4,3,1,5,0,3,2,1,10,19,2,9,19,23,1,9,23,27,2,27,9,31,1,31,5,35,2,35,9,39,1,39,10,43,2,43,13,47,1,47,6,51,2,51,10,55,1,9,55,59,2,6,59,63,1,63,6,67,1,67,10,71,1,71,10,75,2,9,75,79,1,5,79,83,2,9,83,87,1,87,9,91,2,91,13,95,1,95,9,99,1,99,6,103,2,103,6,107,1,107,5,111,1,13,111,115,2,115,6,119,1,119,5,123,1,2,123,127,1,6,127,0,99,2,14,0,0
diff --git a/day02_test.go b/day02_test.go
new file mode 100644
index 0000000..3735818
--- /dev/null
+++ b/day02_test.go
@@ -0,0 +1,47 @@
+package aoc2019
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestExecuteDay02Intcode(t *testing.T) {
+	for codeStr, expResult := range map[string][]int{
+		"1,0,0,0,99":          {2, 0, 0, 0, 99},
+		"2,3,0,3,99":          {2, 3, 0, 6, 99},
+		"2,4,4,5,99,0":        {2, 4, 4, 5, 99, 9801},
+		"1,1,1,4,99,5,6,0,99": {30, 1, 1, 4, 2, 5, 6, 0, 99},
+	} {
+		code, err := parseDay02Intcode(codeStr)
+		if err != nil {
+			t.Fatalf("Parsing Intcode failed: %s", err)
+		}
+
+		res, err := executeDay02Intcode(code)
+		if err != nil {
+			t.Fatalf("Intcode execution failed: %s", err)
+		}
+
+		if !reflect.DeepEqual(res, expResult) {
+			t.Errorf("Intcode execution yield unexpected result: %+v != %+v", res, expResult)
+		}
+	}
+}
+
+func TestCalculateDay2_Part1(t *testing.T) {
+	codeP0, err := solveDay2Part1("day02_input.txt")
+	if err != nil {
+		t.Fatalf("Day 2 solver failed: %s", err)
+	}
+
+	t.Logf("Solution Day 2 Part 1: %d", codeP0)
+}
+
+func TestCalculateDay2_Part2(t *testing.T) {
+	result, err := solveDay2Part2("day02_input.txt")
+	if err != nil {
+		t.Fatalf("Day 2 solver failed: %s", err)
+	}
+
+	t.Logf("Solution Day 2 Part 2: %d", result)
+}