From 91725fbb82a4c72cc327ae5d3dc5d3a3249d1535 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=F0=9F=90=99PiperYxzzy?= <piper@yxzzy.wtf>
Date: Mon, 4 Dec 2023 16:35:41 +0200
Subject: [PATCH] AoC Day 4, Part 2 (Solved)

---
 2023/04/code.go | 51 +++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 47 insertions(+), 4 deletions(-)

diff --git a/2023/04/code.go b/2023/04/code.go
index 196715b..2450a24 100644
--- a/2023/04/code.go
+++ b/2023/04/code.go
@@ -18,14 +18,57 @@ func main() {
 // 4. with: true (part2), and user input
 // the return value of each run is printed to stdout
 func run(part2 bool, input string) any {
-	// when you're ready to do part 2, remove this "not implemented" block
+	gameIdRxp := regexp.MustCompile(`Card +(?P<ID>\d+):  ?(?P<Winning>.*) \|  ?(?P<Drawn>.*)`)
+
 	if part2 {
-		return "not implemented"
+		lines := strings.Split(strings.Trim(input, "\n"), "\n")
+
+		points := make([]int, len(lines))
+		for i, line := range lines {
+
+			matches := gameIdRxp.FindStringSubmatch(line)
+			if len(matches) == 0 {
+				continue
+			}
+
+			winning := strings.Split(matches[2], " ")
+			drawn := strings.Split(matches[3], " ")
+
+			points[i] = 0
+			for _, win := range winning {
+				if win == "" {
+					continue
+				}
+
+				for _, draw := range drawn {
+					if win == draw {
+						points[i] += 1
+					}
+				}
+			}
+		}
+
+		copies := make([]int, len(points))
+		for i := range points {
+			copies[i] = 1
+		}
+		for i, p := range points {
+			for j := i + 1; int(j) <= int(i)+p; j++ {
+				if j < len(copies) {
+					copies[j] += copies[i]
+				}
+			}
+		}
+
+		totalCards := int(0)
+		for _, count := range copies {
+			totalCards += count
+		}
+
+		return totalCards
 	}
 	// solve part 1 here
 
-	gameIdRxp := regexp.MustCompile(`Card +(?P<ID>\d+):  ?(?P<Winning>.*) \|  ?(?P<Drawn>.*)`)
-
 	sum := 0
 	for _, line := range strings.Split(input, "\n") {