Day 18: Part 1 and 2

Signed-off-by: James Griffin <james@unsupervised.ca>

eighteen/day_eighteen.go

@@ -0,0 +1,181 @@
+package eighteen
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type worksheet struct {
+	problems []problem
+}
+
+type problem struct {
+	lhs      int
+	lhsP     *problem
+	operator string
+	rhs      *problem
+}
+
+func parse(input string) *problem {
+	p := problem{}
+	value := ""
+	operation := false
+
+	for i := 0; i < len(input); i++ {
+		switch string(input[i]) {
+		case " ":
+			v, _ := strconv.Atoi(value)
+			p.lhs = v
+		case "*", "+":
+			p.operator = string(input[i])
+			operation = true
+		case "(":
+			p.lhsP = parse(input[i+1:])
+			chars := 0
+			b := 1
+			for j := i + 1; j < len(input); j++ {
+				chars++
+				if string(input[j]) == "(" {
+					b++
+				} else if string(input[j]) == ")" {
+					b--
+				}
+				if b == 0 {
+					break
+				}
+			}
+			i += chars
+		case ")":
+			v, _ := strconv.Atoi(value)
+			p.lhs = v
+			return &p
+		default:
+			value += string(input[i])
+		}
+
+		if operation {
+			p.rhs = parse(input[i+2:])
+			return &p
+		}
+	}
+	v, _ := strconv.Atoi(value)
+	p.lhs = v
+
+	return &p
+}
+
+func (p *problem) eval() int {
+	result := p.lhs
+	if p.lhsP != nil {
+		result = p.lhsP.eval()
+	}
+
+	op := p.operator
+	next := p.rhs
+	for next != nil {
+		v := next.lhs
+		if next.lhsP != nil {
+			v = next.lhsP.eval()
+		}
+		switch op {
+		case "+":
+			result += v
+		case "*":
+			result *= v
+		}
+
+		op = next.operator
+		next = next.rhs
+	}
+
+	return result
+}
+
+func (p *problem) advEval() int {
+	sums := []int{}
+	result := p.lhs
+	if p.lhsP != nil {
+		result = p.lhsP.advEval()
+	}
+
+	op := p.operator
+	next := p.rhs
+	for next != nil {
+		v := next.lhs
+		if next.lhsP != nil {
+			v = next.lhsP.advEval()
+		}
+		switch op {
+		case "+":
+			result += v
+		case "*":
+			sums = append(sums, result)
+			result = v
+		}
+
+		if next.rhs == nil {
+			sums = append(sums, result)
+		}
+
+		op = next.operator
+		next = next.rhs
+	}
+
+	product := 1
+	for _, sum := range sums {
+		product *= sum
+	}
+
+	return product
+}
+
+func (w *worksheet) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		w.problems = append(w.problems, *parse(scanner.Text()))
+	}
+
+	return nil
+}
+
+func (w *worksheet) sum() int {
+	sum := 0
+	for _, p := range w.problems {
+		sum += p.eval()
+	}
+
+	return sum
+}
+
+func (w *worksheet) advSum() int {
+	sum := 0
+	for _, p := range w.problems {
+		sum += p.advEval()
+	}
+
+	return sum
+}
+
+// PartOne What is the sum of the homework
+func PartOne() string {
+	w := worksheet{}
+	w.load("eighteen/input.txt")
+
+	return fmt.Sprintf("The sum of the homework is %d", w.sum())
+}
+
+// PartTwo What is the advanced sum of the homework
+func PartTwo() string {
+	w := worksheet{}
+	w.load("eighteen/input.txt")
+
+	return fmt.Sprintf("The advanced sum of the homework is %d", w.advSum())
+}