Day 07. part 2

day_07/solution.go

@@ -1,10 +1,19 @@
 package day_07
 
 import (
+	"math"
 	"strconv"
 	"strings"
 )
 
+type Operator int
+
+const (
+	ADD      = iota
+	MULTIPLY = iota
+	CONCAT   = iota
+)
+
 type Equation struct {
 	Result    int
 	Variables []int
@@ -16,40 +25,69 @@ func SolveBasic(input string) int {
 
 	sum := 0
 	for _, equation := range equations {
-		if Solvable(equation) {
+		if Solvable(equation, 2) {
 			sum += equation.Result
 		}
 	}
 	return sum
 }
 
-func Solvable(equation Equation) bool {
-	for i := 0; i < 1<<(len(equation.Variables)-1); i++ {
-		if solvable(equation, i) {
+func Solvable(equation Equation, operators int) bool {
+	for i := 0; i < numberOfSolutions(equation, operators); i++ {
+		if solvable(equation, operators, i) {
 			return true
 		}
 	}
 	return false
 }
 
-func solvable(equation Equation, options int) bool {
+func numberOfSolutions(equation Equation, operators int) int {
+	return int(math.Pow(float64(operators), float64(len(equation.Variables)-1)))
+}
+
+func solvable(equation Equation, operators int, options int) bool {
 	sum := equation.Variables[0]
+
 	for i := 0; i < len(equation.Variables)-1; i++ {
 		if sum > equation.Result {
 			return false
 		}
-		if options&(1<<i) != 0 {
+		operator := options % operators
+		options = options / operators
+
+		switch operator {
+		case ADD:
+			sum += equation.Variables[i+1]
+		case MULTIPLY:
 			sum *= equation.Variables[i+1]
-		} else {
+		case CONCAT:
+			offset := findLarger(equation.Variables[i+1])
+			sum *= offset
 			sum += equation.Variables[i+1]
 		}
 	}
 	return sum == equation.Result
 }
 
+func findLarger(val int) int {
+	larger := 10
+	for val >= larger {
+		larger *= 10
+	}
+	return larger
+}
+
 // task:https://adventofcode.com/2024/day/7#part2
 func SolveComplex(input string) int {
-	return 0
+	equations := loadEquations(input)
+
+	sum := 0
+	for _, equation := range equations {
+		if Solvable(equation, 3) {
+			sum += equation.Result
+		}
+	}
+	return sum
 }
 
 func loadEquations(input string) (equations []Equation) {

day_07/solution_test.go

@@ -18,17 +18,17 @@ func TestBasicSolutionExample(t *testing.T) {
 
 func TestComplexSolutionExample(t *testing.T) {
 	result := day_07.SolveComplex(ExampleData)
-	if result != 6 {
-		t.Fatalf("Expected 6 received %d", result)
+	if result != 11387 {
+		t.Fatalf("Expected 11387 received %d", result)
 	}
 }
 
-func TestSolvableExample(t *testing.T) {
-	result := day_07.Solvable(day_07.Equation{
-		Result:    45694842,
-		Variables: []int{2, 9, 227, 6, 1, 5, 4, 382, 1, 5, 2},
-	})
-	if !result {
-		t.Fatalf("Expected true received false")
+func TestSolvable(t *testing.T) {
+	if !day_07.Solvable(day_07.Equation{
+		Result:    27100,
+		Variables: []int{3, 9, 100},
+	}, 3) {
+		t.Fatalf("Expected true")
 	}
+
 }