add day04 solution.

Author: lizthegrey

2023/day04.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"strconv"
+	"strings"
+)
+
+var inputFile = flag.String("inputFile", "inputs/day04.input", "Relative file path to use as input.")
+
+func main() {
+	flag.Parse()
+	bytes, err := ioutil.ReadFile(*inputFile)
+	if err != nil {
+		return
+	}
+	contents := string(bytes)
+	split := strings.Split(contents, "\n")
+
+	memo := make(map[int][]int)
+	sum := 0
+	pending := make(map[int]int)
+	for i, s := range split[:len(split)-1] {
+		pending[i] = 1
+		parts := strings.Split(s[10:], " | ")
+		winners := make(map[int]bool)
+		for _, v := range strings.Split(parts[0], " ") {
+			if v == "" {
+				continue
+			}
+			w, err := strconv.Atoi(v)
+			if err != nil {
+				log.Fatalf("Failed parsing %s: %v", v, err)
+			}
+			winners[w] = true
+		}
+		var won int
+		for _, v := range strings.Split(parts[1], " ") {
+			if v == "" {
+				continue
+			}
+			w, err := strconv.Atoi(v)
+			if err != nil {
+				log.Fatalf("Failed parsing %s: %v", v, err)
+			}
+			if winners[w] {
+				won++
+				memo[i] = append(memo[i], i+won)
+			}
+		}
+		var value int
+		for j := 0; j < len(memo[i]); j++ {
+			if value == 0 {
+				value = 1
+			} else {
+				value *= 2
+			}
+		}
+		sum += value
+	}
+	fmt.Println(sum)
+
+	inventory := make(map[int]int)
+	for len(pending) != 0 {
+		next := make(map[int]int)
+		for k, v := range pending {
+			inventory[k] += v
+			for _, a := range memo[k] {
+				next[a] += v
+			}
+		}
+		pending = next
+	}
+	var cards int
+	for _, v := range inventory {
+		cards += v
+	}
+	fmt.Println(cards)
+}