day6

day6/main.go

@@ -0,0 +1,152 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+func readLines(filename string) []string {
+	raw, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	return strings.Split(string(raw), "\n")
+}
+
+func main() {
+	filename := "input0.txt"
+	if len(os.Args) > 1 {
+		filename = os.Args[1]
+	}
+	lines := readLines(filename)
+	hw, err := parseHomework(lines)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("%v\n", hw.do())
+	hw2, err := parseWeirdHomework(lines)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("%v\n", hw2.do())
+}
+
+type op uint8
+
+const (
+	STAR op = iota
+	PLUS
+)
+
+type homework struct {
+	cols [][]uint64
+	ops  []op
+}
+
+var spaces = regexp.MustCompile(" +")
+
+func parseHomework(lines []string) (homework, error) {
+	var hw homework
+	var err error
+	for i := 0; i < len(lines)-1; i++ {
+		parts := spaces.Split(strings.TrimSpace(lines[i]), -1)
+		if i == 0 {
+			hw.ops = make([]op, len(parts))
+			hw.cols = make([][]uint64, len(parts))
+			for j := range hw.cols {
+				hw.cols[j] = make([]uint64, len(lines)-1)
+			}
+		}
+		for j, part := range parts {
+			hw.cols[j][i], err = strconv.ParseUint(part, 10, 64)
+			if err != nil {
+				return hw, err
+			}
+		}
+	}
+	parts := spaces.Split(strings.TrimSpace(lines[len(lines)-1]), -1)
+	for j, part := range parts {
+		var op op
+		switch part {
+		case "*":
+			op = STAR
+		case "+":
+			op = PLUS
+		default:
+			return hw, fmt.Errorf("invalid op")
+		}
+		hw.ops[j] = op
+	}
+	return hw, nil
+}
+
+func parseWeirdHomework(lines []string) (homework, error) {
+	var hw homework
+	hw.ops = []op{}
+	hw.cols = [][]uint64{}
+	c := 0
+	hw.cols = append(hw.cols, []uint64{})
+	for i := len(lines[0]) - 1; i >= 0; i-- {
+		value := uint64(0)
+		foundValue := false
+		for j := 0; j < len(lines)-1; j++ {
+			line := lines[j]
+			char := line[i]
+			switch char {
+			case ' ':
+				continue
+			default:
+				digit, err := strconv.ParseUint(string(char), 10, 4)
+				if err != nil {
+					return hw, err
+				}
+				foundValue = true
+				value = value*10 + digit
+			}
+		}
+		if foundValue {
+			hw.cols[c] = append(hw.cols[c], value)
+		} else {
+			c++
+			hw.cols = append(hw.cols, []uint64{})
+		}
+	}
+	parts := spaces.Split(strings.TrimSpace(lines[len(lines)-1]), -1)
+	for i := len(parts) - 1; i >= 0; i-- {
+		var op op
+		switch parts[i] {
+		case "*":
+			op = STAR
+		case "+":
+			op = PLUS
+		default:
+			return hw, fmt.Errorf("invalid op")
+		}
+		hw.ops = append(hw.ops, op)
+	}
+	return hw, nil
+}
+
+func (hw homework) do() uint64 {
+	total := uint64(0)
+	for i, col := range hw.cols {
+		op := hw.ops[i]
+		value := uint64(0)
+		switch op {
+		case PLUS:
+			for _, x := range col {
+				value += x
+			}
+		case STAR:
+			value = 1
+			for _, x := range col {
+				value *= x
+			}
+		}
+		total += value
+	}
+	return total
+}