2025 day 5

Author: lucianoq

2025/5/Makefile

@@ -0,0 +1,20 @@
+input:
+	http "https://adventofcode.com/2025/day/5/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
+

2025/5/common.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type Range struct{ Start, End int }
+
+func parseInput() ([]Range, []int) {
+	scanner := bufio.NewScanner(os.Stdin)
+
+	// Scan ranges
+	var ranges []Range
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if line == "" {
+			break
+		}
+
+		ff := strings.Split(line, "-")
+		start, _ := strconv.Atoi(ff[0])
+		end, _ := strconv.Atoi(ff[1])
+		ranges = append(ranges, Range{start, end})
+	}
+
+	// Scan IDs
+	var ids []int
+	for scanner.Scan() {
+		line := scanner.Text()
+		id, _ := strconv.Atoi(line)
+		ids = append(ids, id)
+	}
+
+	return ranges, ids
+}

2025/5/main1.go

@@ -0,0 +1,25 @@
+package main
+
+import "fmt"
+
+func main() {
+	ranges, ids := parseInput()
+
+	count := 0
+	for _, id := range ids {
+		if fresh(ranges, id) {
+			count++
+		}
+	}
+
+	fmt.Println(count)
+}
+
+func fresh(ranges []Range, id int) bool {
+	for _, r := range ranges {
+		if id >= r.Start && id <= r.End {
+			return true
+		}
+	}
+	return false
+}

2025/5/main2.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+func main() {
+	ranges, _ := parseInput()
+
+	sort.Slice(ranges, func(i, j int) bool {
+		if ranges[i].Start == ranges[j].Start {
+			// when they have the same start, prefer bigger ranges on the left,
+			// so `contains` will eat them at the beginning of the next loop
+			return ranges[i].End > ranges[j].End
+		}
+		return ranges[i].Start < ranges[j].Start
+	})
+
+	// index of the Work in Progress range
+	wipIdx := 0
+
+	for i := 1; i < len(ranges); i++ {
+		wipRange := ranges[wipIdx]
+
+		// if the WIP contains the current, we ignore the current
+		if wipRange.contains(ranges[i]) {
+			continue
+		}
+
+		// if they touch, we merge them inside the WIP
+		if wipRange.overlaps(ranges[i]) {
+			ranges[wipIdx] = wipRange.append(ranges[i])
+			continue
+		}
+
+		// disjoint ranges
+		// freeze the current WIP by focusing on the next one
+		// that is the current range
+		wipIdx++
+		ranges[wipIdx] = ranges[i]
+	}
+
+	ranges = ranges[:wipIdx+1]
+
+	sum := 0
+	for _, r := range ranges {
+		sum += r.Len()
+	}
+
+	fmt.Println(sum)
+}
+
+func (r Range) overlaps(r2 Range) bool {
+	return r.Start <= r2.Start && r.End >= r2.Start
+}
+
+func (r Range) contains(r2 Range) bool {
+	return r.Start <= r2.Start && r.End >= r2.End
+}
+
+func (r Range) append(r2 Range) Range {
+	return Range{r.Start, r2.End}
+}
+
+func (r Range) Len() int {
+	return r.End - r.Start + 1
+}