2025 day 6

Author: lucianoq

2025/6/Makefile

@@ -0,0 +1,20 @@
+input:
+	http "https://adventofcode.com/2025/day/6/input" "Cookie:session=${AOC_SESSION};" >input
+
+main1:
+	go build -o main1 main1.go common.go
+
+main2:
+	go build -o main2 main2.go common.go
+
+.PHONY: run1 run2 clean
+
+run1: main1 input
+	./main1 <input
+
+run2: main2 input
+	./main2 <input
+
+clean:
+	rm -f main1 main2 input
+

2025/6/common.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"bufio"
+	"os"
+)
+
+var neutral = map[byte]int{
+	'+': 0,
+	'*': 1,
+}
+
+var fn = map[byte]func(int, int) int{
+	'+': func(a, b int) int { return a + b },
+	'*': func(a, b int) int { return a * b },
+}
+
+func parseInput() []string {
+	var lines []string
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+	return lines
+}

2025/6/main1.go

@@ -0,0 +1,39 @@
+package main
+
+import "fmt"
+
+func main() {
+	lines := parseInput()
+	ops, lines := lines[len(lines)-1], lines[:len(lines)-1]
+
+	grandTotal := 0
+	for i := 0; i < len(ops); i++ {
+		if ops[i] == '*' || ops[i] == '+' {
+			grandTotal += applyHorizontal(lines, i, ops[i])
+		}
+	}
+	fmt.Println(grandTotal)
+}
+
+func applyHorizontal(lines []string, idx int, op byte) int {
+	result := neutral[op]
+	for _, line := range lines {
+		num := readHorizontal(line, idx)
+		result = fn[op](result, num)
+	}
+	return result
+}
+
+func readHorizontal(line string, idx int) int {
+	num := 0
+	for line[idx] == ' ' {
+		idx++
+	}
+	for i := idx; i < len(line); i++ {
+		if line[i] < '0' || line[i] > '9' {
+			break
+		}
+		num = 10*num + int(line[i]-'0')
+	}
+	return num
+}

2025/6/main2.go

@@ -0,0 +1,44 @@
+package main
+
+import "fmt"
+
+func main() {
+	lines := parseInput()
+	ops, lines := lines[len(lines)-1], lines[:len(lines)-1]
+
+	grandTotal := 0
+	for i := 0; i < len(ops); i++ {
+		if ops[i] == '*' || ops[i] == '+' {
+			var j int
+			for j = i + 1; j < len(ops); j++ {
+				if ops[j] == '*' || ops[j] == '+' {
+					j--
+					break
+				}
+			}
+			grandTotal += applyVertical(lines, i, j, ops[i])
+		}
+	}
+
+	fmt.Println(grandTotal)
+}
+
+func applyVertical(lines []string, i, j int, op byte) int {
+	result := neutral[op]
+	for k := i; k < j; k++ {
+		num := readVertical(lines, k)
+		result = fn[op](result, num)
+	}
+	return result
+}
+
+func readVertical(lines []string, idx int) int {
+	num := 0
+	for _, line := range lines {
+		if line[idx] == ' ' {
+			continue
+		}
+		num = num*10 + int(line[idx]-'0')
+	}
+	return num
+}