day 4: only calculate unmarked_sum when needed

1 files changed, 4 insertions, 4 deletions

diff --git a/4.py b/4.py
index e85f358..c75706c 100644
--- a/4.py
+++ b/4.py
@@ -4,7 +4,6 @@ class Board:
     col_hits: list[int]
     row_hits: list[int]
     has_bingo: bool
-    unmarked_sum: int
     nums: dict[int, tuple[int, int]]
     def __init__(self, cells: list[list[int]]) -> None:
         width: int = len(cells[0])
@@ -15,19 +14,20 @@ class Board:
         for y, row in enumerate(cells):
             for x, cell in enumerate(row):
                 self.nums[cell] = (x, y)
-        self.unmarked_sum = sum(self.nums.keys())
         self.has_bingo = False
     def call(self, num: int) -> None:
-        pos: tuple[int, int] = self.nums.get(num)
+        pos: tuple[int, int] | None = self.nums.pop(num, None)
         if pos is None: return
         self.col_hits[pos[0]] -= 1
         self.row_hits[pos[1]] -= 1
-        self.unmarked_sum -= num
         self.has_bingo = (
             self.has_bingo or
             not self.col_hits[pos[0]] or
             not self.row_hits[pos[1]]
         )
+    @property
+    def unmarked_sum(self) -> int:
+        return sum(self.nums.keys())
     @staticmethod
     def from_string(s: str) -> 'Board':
         return Board([[int(n) for n in l.split()] for l in s.split('\n')])