From 6af666ac392c6b26aa42f7e8e4dde630f351b2d4 Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Mon, 21 Dec 2020 22:39:08 -0500
Subject: [PATCH] 2016-day05: md5 hashing, slowww

---
 2016/day05/main.go      | 55 +++++++++++++++++++++++++++++++++++++++++
 2016/day05/main_test.go | 28 +++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 2016/day05/main.go
 create mode 100644 2016/day05/main_test.go

diff --git a/2016/day05/main.go b/2016/day05/main.go
new file mode 100644
index 0000000..2e2a235
--- /dev/null
+++ b/2016/day05/main.go
@@ -0,0 +1,55 @@
+package main
+
+import (
+	"crypto/md5"
+	"flag"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"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 := md5Chess(util.ReadFile("./input.txt"), part)
+	util.CopyToClipboard(fmt.Sprintf("%v", ans))
+	fmt.Println("Output:", ans)
+}
+
+func md5Chess(input string, part int) string {
+	passwordParts := map[int]string{}
+	var part1Index int
+
+	for i := 0; len(passwordParts) < 8; i++ {
+		in := fmt.Sprintf("%s%d", input, i)
+		hash := fmt.Sprintf("%x", md5.Sum([]byte(in)))
+
+		if strings.HasPrefix(hash, "00000") {
+			if part == 1 {
+				passwordParts[part1Index] = hash[5:6]
+				part1Index++
+			} else {
+				if regexp.MustCompile("[0-7]").MatchString(hash[5:6]) {
+					index := cast.ToInt(hash[5:6])
+					if _, ok := passwordParts[index]; !ok {
+						value := hash[6:7]
+						passwordParts[index] = value
+					}
+				}
+			}
+		}
+	}
+
+	var password string
+	for i := 0; i < 8; i++ {
+		password += passwordParts[i]
+	}
+
+	return password
+}
diff --git a/2016/day05/main_test.go b/2016/day05/main_test.go
new file mode 100644
index 0000000..0f34f1b
--- /dev/null
+++ b/2016/day05/main_test.go
@@ -0,0 +1,28 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_md5Chess(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  string
+	}{
+		{"example_part1", "abc", 1, "18f47a30"},
+		{"actual_part1", util.ReadFile("input.txt"), 1, "801b56a7"},
+		{"example_part2", "abc", 2, "05ace8e3"},
+		{"actual_part2", "abc", 2, "424a0197"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := md5Chess(tt.input, tt.part); got != tt.want {
+				t.Errorf("md5Chess() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}