2025 day 1

Author: lucianoq

2025/1/Makefile

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

2025/1/main1.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func main() {
+
+	var (
+		pos   = 50
+		count = 0
+	)
+
+	for scanner := bufio.NewScanner(os.Stdin); scanner.Scan(); {
+		line := scanner.Text()
+
+		steps, _ := strconv.Atoi(line[1:])
+
+		// ignore the loops and keep only the meaningful steps
+		steps = steps % 100
+
+		if line[0] == 'L' {
+			steps *= -1
+		}
+
+		pos = (pos + steps + 100) % 100
+
+		if pos == 0 {
+			count++
+		}
+	}
+
+	fmt.Println(count)
+}

2025/1/main2.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func main() {
+
+	var (
+		pos    = 50
+		oldPos = 50
+		count  = 0
+	)
+
+	for scanner := bufio.NewScanner(os.Stdin); scanner.Scan(); {
+		line := scanner.Text()
+		steps, _ := strconv.Atoi(line[1:])
+
+		// full loops of the command itself
+		count += steps / 100
+
+		// ignore the loops and keep only the meaningful steps
+		steps = steps % 100
+
+		if line[0] == 'L' {
+			steps *= -1
+		}
+
+		oldPos = pos
+		pos += steps
+
+		switch {
+		case pos == 0:
+			count++
+
+		case pos < 0:
+			// If I'm starting from 0, I should not count the passage
+			if oldPos != 0 {
+				count++
+			}
+			pos += 100
+
+		case pos > 99:
+			count++
+			pos -= 100
+		}
+	}
+
+	fmt.Println(count)
+}