[2024] Solution for Day 7

Author: kfarnung

2024/day07/main.go

@@ -0,0 +1,130 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+type equation struct {
+	testValue int64
+	operands  []int64
+}
+
+func part1(input string) int64 {
+	equations, err := parseInput(input)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	sum := int64(0)
+	for _, equation := range equations {
+		if isValidEquation(0, equation.operands, equation.testValue, false) {
+			sum += equation.testValue
+		}
+	}
+
+	return sum
+}
+
+func part2(input string) int64 {
+	equations, err := parseInput(input)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	sum := int64(0)
+	for _, equation := range equations {
+		if isValidEquation(0, equation.operands, equation.testValue, true) {
+			sum += equation.testValue
+		}
+	}
+
+	return sum
+}
+
+func isValidEquation(current int64, operands []int64, target int64, allowConcat bool) bool {
+	if len(operands) == 0 {
+		return current == target
+	}
+
+	operand := operands[0]
+	operands = operands[1:]
+
+	if isValidEquation(current+operand, operands, target, allowConcat) {
+		return true
+	}
+
+	if allowConcat {
+		if isValidEquation(current*getMultiplier(operand)+operand, operands, target, allowConcat) {
+			return true
+		}
+	}
+
+	if current == 0 {
+		current = 1
+	}
+
+	if isValidEquation(current*operand, operands, target, allowConcat) {
+		return true
+	}
+
+	return false
+}
+
+func getMultiplier(num int64) int64 {
+	if num == 0 {
+		return 1
+	}
+
+	multiplier := int64(1)
+	for num > 0 {
+		num /= 10
+		multiplier *= 10
+	}
+
+	return multiplier
+}
+
+func parseInput(input string) ([]equation, error) {
+	var equations []equation
+	for _, line := range lib.SplitLines(input) {
+		before, after, found := strings.Cut(line, ": ")
+		if !found {
+			continue
+		}
+
+		testValue, err := lib.ParseInt[int64](before)
+		if err != nil {
+			return nil, err
+		}
+
+		var operands []int64
+		for _, operandValue := range strings.Split(after, " ") {
+			operand, err := lib.ParseInt[int64](operandValue)
+			if err != nil {
+				return nil, err
+			}
+
+			operands = append(operands, operand)
+		}
+
+		equations = append(equations, equation{testValue: testValue, operands: operands})
+	}
+
+	return equations, nil
+}
+
+func main() {
+	name := os.Args[1]
+	content, err := lib.LoadFileContent(name)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(content))
+	fmt.Printf("Part 2: %d\n", part2(content))
+}

2024/day07/main_test.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"190: 10 19",
+	"3267: 81 40 27",
+	"83: 17 5",
+	"156: 15 6",
+	"7290: 6 8 6 15",
+	"161011: 16 10 13",
+	"192: 17 8 14",
+	"21037: 9 7 18 13",
+	"292: 11 6 16 20",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(3749), part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(3598800864292), part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, int64(11387), part2(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(340362529351427), part2(inputContent))
+}