diff --git a/2021/d04/ex2/ex2.py b/2021/d04/ex2/ex2.py
new file mode 100755
index 0000000..9928698
--- /dev/null
+++ b/2021/d04/ex2/ex2.py
@@ -0,0 +1,69 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from typing import List, Tuple
+
+Board = List[List[int]]
+
+
+def solve(input: List[str]) -> int:
+    def parse_input() -> Tuple[List[int], List[Board]]:
+        def listify(line: str, delim: str = " ") -> List[int]:
+            return [int(n) for n in line.split(delim) if n != ""]
+
+        draw_order = listify(input[0], delim=",")
+        boards: List[Board] = []
+        for l in input[1:]:
+            if l == "":
+                boards.append([])
+                continue
+            boards[-1].append(listify(l))
+
+        return draw_order, boards
+
+    def bingo(board: Board, draw: List[int]) -> bool:
+        assert len(board) == len(board[0])
+
+        def line(l: int) -> bool:
+            return all(n in draw for n in board[l])
+
+        def row(r: int) -> bool:
+            return all(board[i][r] in draw for i in range(len(board)))
+
+        lines = [line(i) for i in range(len(board))]
+        rows = [row(i) for i in range(len(board[0]))]
+
+        return any(itertools.chain(lines, rows))
+
+    draw_order, boards = parse_input()
+
+    draw = []
+    losers = set(range(len(boards)))
+
+    for d in draw_order:
+        draw.append(d)
+        for i, b in enumerate(boards):
+            # Stop early if we already know this board wins
+            if i not in losers:
+                continue
+            if not bingo(b, draw):
+                continue
+            # Discard winners until the last one
+            if len(losers) != 1:
+                losers.discard(i)
+                continue
+            # At thid point, we must be looking at the last winning board
+            return d * sum(n for n in itertools.chain.from_iterable(b) if n not in draw)
+
+    # Sanity check
+    assert False
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()