2016-day14: more md5 stuff

2016/day14/main.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"crypto/md5"
+	"flag"
+	"fmt"
+	"regexp"
+	"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)
+
+	ans := oneTimePad(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func oneTimePad(input string, part int) int {
+	hashCycles := 1
+	if part == 2 {
+		hashCycles = 2016 + 1
+	}
+
+	hashes := []string{}
+	for i := 0; i < 1000; i++ {
+		hashes = append(hashes, hash(input, i, hashCycles))
+	}
+	var keys []int
+	for index := 0; len(keys) < 64; index++ {
+		currentHash := hashes[0]
+
+		// maintain the next 1000 hashes
+		hashes = append(hashes, hash(input, index+1000, hashCycles))
+		hashes = hashes[1:]
+
+		if char := hasTriple(currentHash); char != "" {
+			// this is slow... but it's simple
+			pattern := regexp.MustCompile(fmt.Sprintf("[%s]{5}", char))
+			if pattern.MatchString(strings.Join(hashes, ",")) {
+				keys = append(keys, index)
+			}
+		}
+	}
+
+	return keys[len(keys)-1]
+}
+
+func hash(input string, index, cycles int) string {
+	hashed := fmt.Sprintf("%s%d", input, index)
+	for i := 0; i < cycles; i++ {
+		hashed = fmt.Sprintf("%x", md5.Sum([]byte(hashed)))
+	}
+	return hashed
+}
+
+func hasTriple(in string) string {
+	for i := 2; i < len(in); i++ {
+		if in[i-2] == in[i-1] && in[i-1] == in[i] {
+			return string(in[i])
+		}
+	}
+	return ""
+}

2016/day14/main_test.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"example_part1", "abc", 1, 22728},
+		{"actual_part1", util.ReadFile("input.txt"), 1, 23769},
+		{"example_part2", "abc", 2, 22551},
+		{"actual_part2", util.ReadFile("input.txt"), 2, 20606},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := oneTimePad(tt.input, tt.part); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}