From e0c8c870b0cb65173ed7acbd64f9e6a59e7950c3 Mon Sep 17 00:00:00 2001
From: Simon <hello@gamersi.at>
Date: Mon, 9 Dec 2024 20:24:12 +0100
Subject: [PATCH] day09p2

---
 day09p2/solution.go      | 93 ++++++++++++++++++++++++++++++++++++++++
 day09p2/solution_test.go | 33 ++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 day09p2/solution.go
 create mode 100644 day09p2/solution_test.go

diff --git a/day09p2/solution.go b/day09p2/solution.go
new file mode 100644
index 0000000..32c9947
--- /dev/null
+++ b/day09p2/solution.go
@@ -0,0 +1,93 @@
+package day09p2
+
+import (
+	"io"
+	"strconv"
+
+	"aoc/utils"
+)
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+	line := lines[0]
+
+	return chksum(defrag(line))
+}
+
+func defrag(input string) []int {
+	var result []int
+
+	id := 0
+
+	for i, c := range input {
+		convInt, _ := strconv.Atoi(string(c))
+		storageblock := i%2 == 0
+		for j := 0; j < convInt; j++ {
+			if storageblock {
+				result = append(result, id)
+			} else {
+				result = append(result, -1)
+			}
+		}
+		if storageblock {
+			id++
+		}
+	}
+
+	fileCount := id
+	for fileID := fileCount - 1; fileID >= 0; fileID-- {
+		fileStart, fileEnd := -1, -1
+		for i := 0; i < len(result); i++ {
+			if result[i] == fileID {
+				if fileStart == -1 {
+					fileStart = i
+				}
+				fileEnd = i
+			}
+		}
+		if fileStart == -1 {
+			continue
+		}
+
+		fileLength := fileEnd - fileStart + 1
+
+		freeStart, freeLength := -1, 0
+		for i := 0; i < len(result); i++ {
+			if result[i] == -1 {
+				if freeStart == -1 {
+					freeStart = i
+				}
+				freeLength++
+				if freeLength >= fileLength {
+					break
+				}
+			} else {
+				freeStart = -1
+				freeLength = 0
+			}
+		}
+
+		if freeLength >= fileLength && freeStart != -1 && freeStart < fileStart {
+			for i := 0; i < fileLength; i++ {
+				result[freeStart+i] = fileID
+			}
+			for i := fileStart; i <= fileEnd; i++ {
+				result[i] = -1
+			}
+		}
+	}
+
+	return result
+}
+
+func chksum(input []int) int {
+	sum := 0
+
+	for i, id := range input {
+		if id != -1 {
+			sum += i * id
+		}
+	}
+
+	return sum
+}
diff --git a/day09p2/solution_test.go b/day09p2/solution_test.go
new file mode 100644
index 0000000..78551cd
--- /dev/null
+++ b/day09p2/solution_test.go
@@ -0,0 +1,33 @@
+package day09p2
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `2333133121414131402`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int
+	}{
+		{testInput, 2858},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}