Day 1: Part 1

one/day_one.go

@@ -0,0 +1,67 @@
+package one
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type expenseReport struct {
+	expenses []int
+}
+
+func (e *expenseReport) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		value, err := strconv.Atoi(scanner.Text())
+		if err != nil {
+			return err
+		}
+		e.expenses = append(e.expenses, value)
+	}
+
+	return nil
+}
+
+func (e *expenseReport) searchAndMultiply(target int) (int, error) {
+	for i := 0; i < len(e.expenses); i++ {
+		if e.expenses[i] > target {
+			continue
+		}
+
+		for j := i + 1; j < len(e.expenses); j++ {
+			if e.expenses[j] > target {
+				continue
+			}
+
+			if (e.expenses[i] + e.expenses[j]) == target {
+				return e.expenses[i] * e.expenses[j], nil
+			}
+		}
+	}
+
+	return -1, fmt.Errorf("Unable to find target pair that sums to %d", target)
+}
+
+// PartOne Find the multiplied value of the two expenses totalling 2020
+func PartOne() string {
+	report := expenseReport{}
+	err := report.load("one/expenses.txt")
+	if err != nil {
+		return fmt.Sprintf("Unable to load expenses: %s", err.Error())
+	}
+
+	result, err := report.searchAndMultiply(2020)
+	if err != nil {
+		return err.Error()
+	}
+
+	return fmt.Sprintf("The output of the expenses summing to 2020 is %d", result)
+}