Solve 2023:04 "Scratchcards"

On a train that according to swedish tradition
was late. Not a good environment to focus.

Got stuck 2 times:

- Initial code asumed the | was always after the 5th
  number, because of the example. Puzzle input had
  it at pos 10. Classic AoC mistake.
- I had a hard time trying to understand the score
  count, I insisted there was meant to be a +1 at
  some point.

  > That means card 1 is worth 8 points (1 for
  > the first match, then doubled three times for
  > each of the three matches after the first)

I should instead have just looked at the numbers.

2023-python/output/day_04.py

@@ -0,0 +1,50 @@
+import re
+from collections import defaultdict
+from output import answer, puzzleinput
+
+n = 4
+title = "Scratchcards"
+
+
+@answer(1, "Sum of all scratchcard points are {}")
+def part_1(presolved):
+    scores, _ = presolved
+    return scores
+
+
+@answer(2, "Ends up wih a total of {} scratchcards")
+def part_2(presolved):
+    _, count = presolved
+    return count
+
+
+@puzzleinput(n)
+def parse_input(data):
+    return data
+
+
+def presolve(data):
+    scores = []
+    count = defaultdict(int)
+    for cid, line in enumerate(data.splitlines()):
+        a, b = line.split("|")
+        a = set(re.findall(r"\d+", a)[1:])
+        b = set(re.findall(r"\d+", b))
+        ab = len(a & b)
+        if ab > 0:
+            scores.append(2**(ab - 1))
+        count[cid] += 1
+        for i in range(cid + 1, cid + ab + 1):
+            count[i] += count[cid]
+    return sum(scores), sum(count.values())
+
+
+if __name__ == "__main__":
+    inp = parse_input()
+    inp = presolve(inp)
+
+    a = part_1(inp)
+    b = part_2(inp)
+
+    assert a == 21919
+    assert b == 9881048