🌅

solutions/day4/day4.go

@@ -0,0 +1,114 @@
+package day4
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type SectionRange struct {
+	start int
+	end   int
+}
+
+func total_overlap(a SectionRange, b SectionRange) bool {
+	return ((a.start >= b.start) && (a.end <= b.end)) ||
+		((b.start >= a.start) && (b.end <= a.end))
+}
+
+func partial_overlap(a SectionRange, b SectionRange) bool {
+	return (a.start >= b.start && a.start <= b.end) ||
+		(a.end >= b.end && a.end <= b.end) ||
+		(b.start >= a.start && b.start <= a.end) ||
+		(b.end >= a.start && b.end <= a.end)
+}
+
+func range_from_string(s string) (ret_range SectionRange, err error) {
+	ret_range = SectionRange{0, 0}
+	items := strings.Split(s, "-")
+
+	if len(items) != 2 {
+		err = errors.New("invalid range format")
+		return
+	}
+
+	start, start_err := strconv.Atoi(items[0])
+	if start_err != nil {
+		err = start_err
+		return
+	}
+	ret_range.start = start
+
+	end, end_err := strconv.Atoi(items[1])
+	if end_err != nil {
+		err = end_err
+		return
+	}
+	ret_range.end = end
+
+	err = nil
+
+	return
+}
+
+func line_to_pair(s string) (left SectionRange, right SectionRange, err error) {
+	items := strings.Split(s, ",")
+
+	if len(items) != 2 {
+		err = errors.New("invalid range format")
+		return
+	}
+
+	left, left_err := range_from_string(items[0])
+	if left_err != nil {
+		err = left_err
+		return
+	}
+
+	right, right_err := range_from_string(items[1])
+	if right_err != nil {
+		err = right_err
+		return
+	}
+
+	return
+}
+
+func Run(filename string) {
+	file, err := os.Open(filename)
+
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	var total_overlapping int = 0
+	var partial_overlapping int = 0
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		left, right, err := line_to_pair(line)
+
+		if err != nil {
+			fmt.Println("ERROR: failed to parse line:", err)
+		} else {
+			if total_overlap(left, right) {
+				total_overlapping += 1
+			}
+
+			if partial_overlap(left, right) {
+				partial_overlapping += 1
+			}
+		}
+	}
+
+	file.Close()
+
+	fmt.Println("# of overlapping pairs", total_overlapping)
+	fmt.Println("# of partially overlapping pairs", partial_overlapping)
+}