first commit

day-01/internal/two/solve.go

@@ -0,0 +1,63 @@
+package two
+
+import (
+	"bufio"
+	"bytes"
+	"embed"
+	"io"
+	"regexp"
+	"slices"
+
+	"github.com/onyx-and-iris/aoc2024/day-01/internal/util"
+)
+
+//go:embed testdata
+var files embed.FS
+
+var reNums = regexp.MustCompile(`[0-9]+`)
+
+func Solve() (int, error) {
+	data, _ := files.ReadFile("testdata/input.txt")
+
+	r := bytes.NewReader(data)
+	left, right, err := parseLines(r)
+	if err != nil {
+		return 0, err
+	}
+
+	var similarity int
+	for k, v := range left {
+		indx := slices.Index(right, k)
+		if indx == -1 {
+			continue
+		}
+
+		var occurrences int
+		for _, n := range right[indx:] {
+			if n == k {
+				occurrences++
+			}
+		}
+		similarity += k * v * occurrences
+	}
+
+	return similarity, nil
+}
+
+func parseLines(r io.Reader) (map[int]int, []int, error) {
+	var left map[int]int = make(map[int]int)
+	var right []int
+
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		nums := reNums.FindAllString(scanner.Text(), -1)
+		left[util.MustConv(nums[0])] = left[util.MustConv(nums[0])] + 1
+		right = util.InsertSorted(right, util.MustConv(nums[1]))
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, nil, err
+	}
+
+	return left, right, nil
+}