day3

day3/main.go

@@ -0,0 +1,147 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func readLines(filename string) []string {
+	raw, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	return strings.Split(string(raw), "\n")
+}
+
+type bank struct {
+	batteries []uint8
+}
+
+func parseLine(line string) (bank, error) {
+	b := bank{
+		batteries: make([]uint8, len(line)),
+	}
+	for i, c := range line {
+		var battery uint8
+		switch c {
+		case '1':
+			battery = 1
+		case '2':
+			battery = 2
+		case '3':
+			battery = 3
+		case '4':
+			battery = 4
+		case '5':
+			battery = 5
+		case '6':
+			battery = 6
+		case '7':
+			battery = 7
+		case '8':
+			battery = 8
+		case '9':
+			battery = 9
+		default:
+			return b, fmt.Errorf("Invalid battery")
+		}
+		b.batteries[i] = battery
+	}
+	return b, nil
+}
+
+func (b bank) findLargestJoltage() uint8 {
+	if len(b.batteries) < 2 {
+		return 0
+	}
+	var first, second uint8
+	for _, battery := range b.batteries {
+		if first == 0 {
+			first = battery
+			continue
+		}
+		if second == 0 {
+			second = battery
+			continue
+		}
+		if second > first {
+			first = second
+			second = battery
+			continue
+		}
+		if battery > second {
+			second = battery
+			continue
+		}
+	}
+	return first*10 + second
+}
+
+// Functionally, append the candidate to the batteries, then
+// remove the first battery preceding an increase in values.
+func addBatteryToMax(batteries []uint8, candidate uint8) {
+	n := uint8(len(batteries))
+	if n == 0 {
+		return
+	}
+	last := batteries[0]
+	for i := uint8(1); i < n; i++ {
+		current := batteries[i]
+		if current > last {
+			// i-1 = current
+			// i:n-2 <- i+1:n-1
+			// n-1 = candidate
+			batteries[i-1] = current
+			for j := i; j <= n-2; j++ {
+				batteries[j] = batteries[j+1]
+			}
+			batteries[n-1] = candidate
+			return
+		}
+		last = current
+	}
+	if candidate > batteries[n-1] {
+		batteries[n-1] = candidate
+	}
+}
+
+func (b bank) findMaximumJoltage(n uint8) uint64 {
+	if len(b.batteries) < int(n) || n == 0 {
+		return 0
+	}
+	max := make([]uint8, n)
+
+	for i := range n {
+		max[i] = b.batteries[i]
+	}
+	for i := n; i < uint8(len(b.batteries)); i++ {
+		addBatteryToMax(max, b.batteries[i])
+	}
+
+	joltage := uint64(0)
+	for _, battery := range max {
+		joltage = joltage*10 + uint64(battery)
+	}
+	return joltage
+}
+
+func main() {
+	filename := "input0.txt"
+	if len(os.Args) > 1 {
+		filename = os.Args[1]
+	}
+	lines := readLines(filename)
+	var total uint
+	var max uint64
+	for _, line := range lines {
+		bank, err := parseLine(line)
+		if err != nil {
+			panic(err)
+		}
+		total += uint(bank.findLargestJoltage())
+		max += bank.findMaximumJoltage(12)
+	}
+	fmt.Printf("%v\n", total)
+	fmt.Printf("%v\n", max)
+}