Add day 4 solution

python/2023/README.org

@@ -21,3 +21,26 @@
 *** Answers
 2600
 86036
+
+** Day 4
+
+#+begin_src shell
+  source ~/virtualenvs/aoc-2023/bin/activate
+  cd ~/git/advent-of-code/python/2023
+  python src/andy_aoc_2023/day4.py src/andy_aoc_2023/day4_big
+#+end_src
+
+Warning: Part 2 is a little slow
+
+#+begin_src shell
+  ~/bin/avg-time 5 python src/andy_aoc_2023/day4.py src/andy_aoc_2023/day4_big
+  real 8.994000
+  user 8.982000
+  sys 0.008000
+#+end_src
+
+where =avg-time= is [[https://stackoverflow.com/a/54920339][this bit of =awk=]]
+
+*** Answers
+19135
+5704953

python/2023/src/andy_aoc_2023/day4.py

@@ -0,0 +1,56 @@
+from collections import defaultdict
+from pprint import pprint
+import re
+import sys
+
+
+def parse_raw_input(lines):
+    output ={}
+    for line in lines:
+        card_num, numbers = line.strip().split(": ")
+        card_id = card_num.split(" ")[-1]
+        winning_nums, our_nums = numbers.split(" | ")
+        output[card_id] = {
+            "win": re.split(r"\s+", winning_nums),
+            "our": re.split(r"\s+", our_nums),
+        }
+    return output
+
+def part_1(input_lines):
+    total = 0
+    for id, cards in input_lines.items():
+        win = set(cards["win"])
+        our = set(cards["our"])
+
+        matches = win.intersection(our)
+        count = val if (val := len(matches)) > 0 else 0
+        points = (2 ** (count - 1) // 1)
+        total += points
+        print(f"Card {id} has {count} {matches} matches, {points} points,  total {total}")
+
+
+def part_2(input_lines):
+    instances = defaultdict(lambda : 0)
+    for id, cards in input_lines.items():
+        instances[id] += 1
+        for _ in range(instances[id]):
+            win = set(cards["win"])
+            our = set(cards["our"])
+
+            matches = win.intersection(our)
+            count = val if (val := len(matches)) > 0 else 0
+
+            for x in range(count):
+                copy_num = int(id) + 1 + x
+                instances[str(copy_num)] += 1
+
+    print(f"Total {sum( x for x in instances.values() )}")
+
+
+input_file = sys.argv[1]
+
+with open(input_file) as infile:
+    input_lines = parse_raw_input(infile.readlines())
+
+part_1(input_lines)
+part_2(input_lines)