Day 9

9/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+)
+
+func main() {
+	numbers := []int{}
+
+	file, _ := os.Open("input.txt")
+	defer file.Close()
+	for scanner := bufio.NewScanner(file); scanner.Scan(); {
+		number, _ := strconv.Atoi(scanner.Text())
+		numbers = append(numbers, number)
+	}
+
+	preambleLength := 25
+	preambleStart := 0
+	invalidNum := 0
+	for i, number := range numbers {
+		if i >= preambleLength {
+			valid := validNumber(preamble(numbers, preambleStart, preambleLength), number)
+			if !valid {
+				invalidNum = number
+				break
+			}
+			preambleStart++
+		}
+	}
+
+	fmt.Println("Part 1:", invalidNum)
+
+	finalSet := []int{}
+outer:
+	for i := 0; i < len(numbers)-1; i++ {
+		for j := len(numbers) - 1; j > i; j-- {
+			if testSet := numbers[i:j]; sum(testSet) == invalidNum {
+				finalSet = testSet
+				break outer
+			}
+		}
+	}
+	sort.Ints(finalSet)
+	weakness := finalSet[0] + finalSet[len(finalSet)-1]
+
+	fmt.Println("Part 2:", weakness)
+
+}
+
+func preamble(n []int, start, length int) []int {
+	return n[start : start+length]
+}
+
+func validNumber(preamble []int, num int) bool {
+	for _, i := range preamble {
+		for _, j := range preamble {
+			if i+j == num && i != j {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func sum(slice []int) int {
+	sum := 0
+	for _, v := range slice {
+		sum += v
+	}
+	return sum
+}