2020 Day 9 Complete

2020/day08/main.go

@@ -8,7 +8,7 @@ import (
 )
 
 func main() {
-	fmt.Println("# Day 7")
+	fmt.Println("# Day 8")
 	inp := h.StdinToStringSlice()
 	FixProg(inp)
 }

2020/day09/main.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	fmt.Println("# Day 9")
+	inp := h.StdinToIntSlice()
+	rogue, err := FindRogueNumber(inp)
+	if err != nil {
+		fmt.Println(err.Error())
+		return
+	}
+	answer, err := FindWeakness(rogue, inp)
+	if err != nil {
+		fmt.Println(err.Error())
+		return
+	}
+	fmt.Println("Answer:", answer)
+}
+
+func FindRogueNumber(inp []int) (int, error) {
+	for k, v := range inp {
+		if k >= 25 {
+			if !ContainsPairFor(v, inp[k-25:k]) {
+				return v, nil
+			}
+		}
+	}
+	return -1, errors.New("All numbers fit")
+}
+
+func ContainsPairFor(target int, inp []int) bool {
+	for i := 0; i < len(inp)-1; i++ {
+		for k := i + 1; k < len(inp); k++ {
+			if inp[i]+inp[k] == target {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func FindWeakness(target int, inp []int) (int, error) {
+	for i := 0; i < len(inp)-1; i++ {
+		for k := i + 1; k < len(inp); k++ {
+			sum := GetSumForRange(inp[i:k])
+			if sum == target {
+				return FindSmallest(inp[i:k]) + FindLargest(inp[i:k]), nil
+			} else if sum > target {
+				break
+			}
+		}
+	}
+	return -1, errors.New("No weakness found")
+}
+
+func GetSumForRange(inp []int) int {
+	var ret int
+	for k := range inp {
+		ret = ret + inp[k]
+	}
+	return ret
+}
+
+func FindSmallest(inp []int) int {
+	ret := inp[0]
+	for k := range inp {
+		if inp[k] < ret {
+			ret = inp[k]
+		}
+	}
+	return ret
+}
+
+func FindLargest(inp []int) int {
+	ret := inp[0]
+	for k := range inp {
+		if inp[k] > ret {
+			ret = inp[k]
+		}
+	}
+	return ret
+}

2020/day09/testinput

@@ -0,0 +1,20 @@
+35
+20
+15
+25
+47
+40
+62
+55
+65
+95
+102
+117
+150
+182
+127
+219
+299
+277
+309
+576