From 27b95e6717314e40c293caeae445df48a12fff1c Mon Sep 17 00:00:00 2001
From: Katherina Walshe-Grey <git@qenya.tel>
Date: Tue, 5 Nov 2024 13:31:09 +0000
Subject: [PATCH] Day 3a

---
 day03/day03.go      | 113 ++++++++++++++++++++++++++++++++++++++++++++
 day03/day03_test.go |  25 ++++++++++
 day03/input.txt     |  10 ++++
 3 files changed, 148 insertions(+)
 create mode 100644 day03/day03.go
 create mode 100644 day03/day03_test.go
 create mode 100644 day03/input.txt

diff --git a/day03/day03.go b/day03/day03.go
new file mode 100644
index 0000000..e0bb49d
--- /dev/null
+++ b/day03/day03.go
@@ -0,0 +1,113 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+
+const DIGITS = "0123456789"
+const SPACE = '.'
+
+type Number struct {
+	number int
+	index int
+	width int
+}
+
+
+func isDigit(in rune) bool {
+	return strings.ContainsRune(DIGITS, in)
+}
+
+func isNotDigit(in rune) bool {
+	return !isDigit(in)
+}
+
+func isSpace(in rune) bool {
+	return in == SPACE
+}
+
+func isPart(in rune) bool {
+	return !isDigit(in) && !isSpace(in)
+}
+
+func hasPartAtPos(line string, at int) bool {
+	return at >= 0 && at < len(line) && isPart(rune(line[at]))
+}
+
+func hasPartInRange(line string, from int, to int) bool {
+	return len(line) > from && strings.ContainsFunc(line[max(from, 0):min(to, len(line))], isPart)
+}
+
+func findNumbers(line string) (numbers []Number) {
+	offset, index := 0, 0
+	for {
+		index = strings.IndexFunc(line[offset:], isDigit)
+		if index == -1 {
+			break
+		}
+		
+		width := strings.IndexFunc(line[offset+index:], isNotDigit)
+		if width == -1 {
+			width = len(line) - offset - index
+		}
+
+		numberA := line[offset+index:offset+index+width]
+		numberI, err := strconv.Atoi(numberA)
+		if err != nil {
+			panic(fmt.Sprintf(`day03: could not parse number: "%s"`, numberA))
+		}
+
+		numbers = append(numbers, Number{numberI, offset+index, width})
+		offset += index + width
+	}
+	return
+}
+
+func ScanFile(file *os.File) (int, error) {
+	scanner := bufio.NewScanner(file)
+	var sum int
+
+	var prevLine string
+	var prevNumbers []Number
+    for scanner.Scan() {
+		line := scanner.Text()
+		numbers := findNumbers(line)
+
+		var unmatchedNumbers []Number
+		for _, v := range numbers {
+			number, index, width := v.number, v.index, v.width
+			if hasPartAtPos(line, index - 1) || hasPartAtPos(line, index + width) || hasPartInRange(prevLine, index - 1, index + width + 1) {
+				sum += number
+			} else {
+				unmatchedNumbers = append(unmatchedNumbers, v)
+			}
+		}
+		for _, v := range prevNumbers {
+			number, index, width := v.number, v.index, v.width
+			if hasPartInRange(line, index - 1, index + width + 1) {
+				sum += number
+			}
+		}
+
+		prevLine = line
+		prevNumbers = unmatchedNumbers
+    }
+    if err := scanner.Err(); err != nil {
+        return 0, err
+    }
+	return sum, nil
+}
+
+func main() {
+	sum, err := ScanFile(os.Stdin)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Invalid input: %s\n", err)
+		return
+	}
+	fmt.Println(sum)
+}
\ No newline at end of file
diff --git a/day03/day03_test.go b/day03/day03_test.go
new file mode 100644
index 0000000..3d2f28c
--- /dev/null
+++ b/day03/day03_test.go
@@ -0,0 +1,25 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestScanFile(t *testing.T) {
+	inFile := "input.txt"
+	want := 4361
+
+	f, err := os.Open(inFile)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := ScanFile(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	
+	if got != want {
+		t.Errorf("ScanFile(%q) == %d, want %d", inFile, got, want)
+	}
+}
\ No newline at end of file
diff --git a/day03/input.txt b/day03/input.txt
new file mode 100644
index 0000000..624ea4f
--- /dev/null
+++ b/day03/input.txt
@@ -0,0 +1,10 @@
+467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..
\ No newline at end of file