Add solution for day 7 part 1

Author: terminalnode

README.md

@@ -51,7 +51,7 @@ automatically rebuilt and redeployed ever time the `common` module or their own
 | 04  | ⭐ ⭐      | 17  |          |
 | 05  | ⭐ ⭐      | 18  |          |
 | 06  | ⭐ ⭐      | 19  |          |
-| 07  |          | 20  |          |
+| 07  | ⭐        | 20  |          |
 | 08  |          | 21  |          |
 | 09  |          | 22  |          |
 | 10  |          | 23  |          |

solutions/day07/main.go

@@ -1,9 +1,83 @@
 package main
 
 import (
+	"fmt"
 	"github.com/terminalnode/adventofcode2024/common"
+	"strconv"
+	"strings"
 )
 
+type equation = struct {
+	Test int
+	Ops  []int
+}
+
 func main() {
-	common.Setup(7, nil, nil)
+	common.Setup(7, part1, nil)
+}
+
+func part1(
+	input string,
+) string {
+	equations, err := parseEquations(input)
+	if err != nil {
+		return fmt.Sprintf("Failed to parse input: %v", err)
+	}
+
+	sum := 0
+	for _, eq := range equations {
+		if validateEquation(eq.Ops[0], eq.Test, eq.Ops[1:]) {
+			sum += eq.Test
+		}
+	}
+
+	return fmt.Sprintf("Sum of all OK tests: %d", sum)
+}
+
+func parseEquations(
+	input string,
+) ([]equation, error) {
+	lines := strings.Split(input, "\n")
+	equations := make([]equation, len(lines))
+	for i, rawEq := range lines {
+		testSplitOps := strings.Split(rawEq, ": ")
+		if len(testSplitOps) != 2 {
+			return equations, fmt.Errorf("splitting %v by ': ' resulted in %d pieces (should be two)", rawEq, len(testSplitOps))
+		}
+
+		test, err := strconv.ParseInt(testSplitOps[0], 10, 0)
+		if err != nil {
+			return equations, err
+		}
+
+		splitOps := strings.Split(testSplitOps[1], " ")
+		ops := make([]int, len(splitOps))
+		for opI, rawOp := range splitOps {
+			op, err := strconv.ParseInt(rawOp, 10, 0)
+			if err != nil {
+				return equations, err
+			}
+			ops[opI] = int(op)
+		}
+
+		equations[i] = equation{int(test), ops}
+	}
+
+	return equations, nil
+}
+
+func validateEquation(
+	currentValue int,
+	targetValue int,
+	operators []int,
+) bool {
+	if currentValue > targetValue {
+		return false
+	} else if len(operators) == 0 {
+		return currentValue == targetValue
+	}
+	next := operators[0]
+	mul := validateEquation(currentValue*next, targetValue, operators[1:])
+	add := validateEquation(currentValue+next, targetValue, operators[1:])
+	return mul || add
 }