Solve 2024 day 7 in go

2024/go/day-07/main.go

@@ -0,0 +1,116 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+type equation struct {
+	result  int
+	numbers []int
+}
+
+func isNotNumber(c rune) bool {
+	return !unicode.IsNumber(c)
+}
+
+func readInput() (equations []equation, err error) {
+	content, err := os.ReadFile("input")
+	if err != nil {
+		return
+	}
+
+	lines := strings.Split(strings.TrimSpace(string(content)), "\n")
+	for _, line := range lines {
+		parts := strings.FieldsFunc(line, isNotNumber)
+		nums := make([]int, len(parts))
+
+		for i, part := range parts {
+			nums[i], _ = strconv.Atoi(part)
+		}
+
+		equations = append(equations, equation{result: nums[0], numbers: nums[1:]})
+	}
+
+	return
+}
+
+func pow(base, exp int) int {
+	result := 1
+	for {
+		if exp&1 == 1 {
+			result *= base
+		}
+		exp >>= 1
+		if exp == 0 {
+			break
+		}
+		base *= base
+	}
+	return result
+}
+
+func equationResult(nums []int, operatorMask, operatorSpace int) int {
+	result := nums[0]
+
+	for operatorIndex := 0; operatorIndex < len(nums)-1; operatorIndex++ {
+		currentOperator := (operatorMask / pow(operatorSpace, operatorIndex)) % operatorSpace
+		currentNum := nums[operatorIndex+1]
+
+		switch currentOperator {
+		case 0:
+			result += currentNum
+		case 1:
+			result *= currentNum
+		case 2:
+			result, _ = strconv.Atoi(fmt.Sprintf("%d%d", result, currentNum))
+		default:
+			panic("Unsupported operator")
+		}
+	}
+
+	return result
+}
+
+func isValidEquation(eq equation, operatorSpace int) bool {
+	maxOperatorMask := pow(operatorSpace, len(eq.numbers)-1) - 1
+
+	for operatorMask := 0; operatorMask <= maxOperatorMask; operatorMask++ {
+		if equationResult(eq.numbers, operatorMask, operatorSpace) == eq.result {
+			return true
+		}
+	}
+
+	return false
+}
+
+func totalResult(equations []equation) (result, resultWithConcat int) {
+	for _, eq := range equations {
+		if isValidEquation(eq, 2) {
+			result += eq.result
+			resultWithConcat += eq.result
+		} else if isValidEquation(eq, 3) {
+			resultWithConcat += eq.result
+		}
+	}
+
+	return
+}
+
+func main() {
+	equations, err := readInput()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	result, resultWithConcat := totalResult(equations)
+
+	// Part one
+	fmt.Println("Total calibration result:", result)
+	// Part two
+	fmt.Println("Total calibration result with concatenation:", resultWithConcat)
+}