From a0ce63e5a514e14e510c4739b4a894ade995767c Mon Sep 17 00:00:00 2001
From: Kharec <sandro@cazzaniga.fr>
Date: Sat, 29 Nov 2025 09:57:54 +0100
Subject: [PATCH] feat: solve d4 both parts using md5 bruteforce

---
 internal/2015/DayFour/code.go | 46 +++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 internal/2015/DayFour/code.go

diff --git a/internal/2015/DayFour/code.go b/internal/2015/DayFour/code.go
new file mode 100644
index 0000000..32aee52
--- /dev/null
+++ b/internal/2015/DayFour/code.go
@@ -0,0 +1,46 @@
+package dayfour
+
+import (
+	"advent-of-code/internal/registry"
+	"bytes"
+	"crypto/md5"
+	"os"
+	"strconv"
+)
+
+func init() {
+	registry.Register("2015D4", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) []byte {
+	content, _ := os.ReadFile(filepath)
+	return bytes.TrimSpace(content)
+}
+
+func findHashWithZeroes(data []byte, zeroes int) int {
+	buffer := make([]byte, len(data), len(data)+10)
+	copy(buffer, data)
+	for idx := 1; ; idx++ {
+		buffer = buffer[:len(data)]
+		buffer = strconv.AppendInt(buffer, int64(idx), 10)
+		hash := md5.Sum(buffer)
+		switch zeroes {
+		case 5:
+			if hash[0] == 0 && hash[1] == 0 && hash[2]&0xF0 == 0 {
+				return idx
+			}
+		case 6:
+			if hash[0] == 0 && hash[1] == 0 && hash[2] == 0 {
+				return idx
+			}
+		}
+	}
+}
+
+func PartOne(data []byte) int {
+	return findHashWithZeroes(data, 5)
+}
+
+func PartTwo(data []byte) int {
+	return findHashWithZeroes(data, 6)
+}