Day 9.

day9/part1/main.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+type validator struct {
+	Numbers []int
+}
+
+func newValidator() *validator {
+	return &validator{
+		Numbers: []int{},
+	}
+}
+
+func (v *validator) validate(number int) (ok bool) {
+	for i1, num1 := range v.Numbers {
+		for i2, num2 := range v.Numbers {
+			if i1 == i2 {
+				continue
+			}
+			if num1+num2 == number {
+				ok = true
+				return
+			}
+		}
+	}
+	return
+}
+
+func (v *validator) Feed(number int) (ok bool) {
+	if len(v.Numbers) >= 25 {
+		// check if valid number
+		if !v.validate(number) {
+			return
+		}
+		v.Numbers = append(v.Numbers[len(v.Numbers)-24:], number)
+	} else {
+		v.Numbers = append(v.Numbers, number)
+	}
+	ok = true
+	return
+}
+
+func main() {
+	f, err := os.Open("input")
+	if err != nil {
+		panic(err)
+	}
+
+	v := newValidator()
+
+	number := 0
+
+	for {
+		_, err := fmt.Fscanf(f, "%d\n", &number)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			panic(err)
+		}
+
+		if !v.Feed(number) {
+			fmt.Printf("%d does not validate\n", number)
+			break
+		}
+	}
+
+}

day9/part2/main.go

@@ -0,0 +1,104 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"math"
+	"os"
+)
+
+type validator struct {
+	Numbers []int
+}
+
+func newValidator() *validator {
+	return &validator{
+		Numbers: []int{},
+	}
+}
+
+func (v *validator) validate(number int) (ok bool) {
+	for i1, num1 := range v.Numbers {
+		for i2, num2 := range v.Numbers {
+			if i1 == i2 {
+				continue
+			}
+			if num1+num2 == number {
+				ok = true
+				return
+			}
+		}
+	}
+	return
+}
+
+func (v *validator) Feed(number int) (ok bool) {
+	if len(v.Numbers) >= 25 {
+		// check if valid number
+		if !v.validate(number) {
+			return
+		}
+		v.Numbers = append(v.Numbers[len(v.Numbers)-24:], number)
+	} else {
+		v.Numbers = append(v.Numbers, number)
+	}
+	ok = true
+	return
+}
+
+func main() {
+	f, err := os.Open("input")
+	if err != nil {
+		panic(err)
+	}
+
+	v := newValidator()
+
+	number := 0
+	allNumbers := []int{}
+
+	for {
+		_, err := fmt.Fscanf(f, "%d\n", &number)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			panic(err)
+		}
+
+		if !v.Feed(number) {
+			fmt.Printf("%d does not validate\n", number)
+			fmt.Printf("%d numbers tracked\n", len(allNumbers))
+
+			// find contiguous set of numbers that add up to this invalid number
+		weaknessloop:
+			for i1 := range allNumbers {
+				for i2 := i1 + 1; i2 < len(allNumbers); i2++ {
+					sum := 0
+					min := math.MaxInt32
+					max := math.MinInt32
+					for i := i1; i <= i2; i++ {
+						newNum := allNumbers[i]
+						if min > newNum {
+							min = newNum
+						}
+						if max < newNum {
+							max = newNum
+						}
+						sum += newNum
+					}
+					if sum == number {
+						fmt.Printf("min: %d\n", min)
+						fmt.Printf("max: %d\n", max)
+						fmt.Printf("weakness: %d\n", min+max)
+						break weaknessloop
+					}
+				}
+			}
+
+			break
+		}
+
+		allNumbers = append(allNumbers, number)
+	}
+}