Add day13

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

day13/day13.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+import sys
+import dataclasses
+import re
+from typing import Sequence, Set, Tuple
+from copy import deepcopy
+
+
+FOLD_RE = re.compile(r"fold along (?P<dir>[xy])=(?P<off>[0-9]+)")
+Point = Tuple[int, int]
+
+
+@dataclasses.dataclass
+class Fold:
+    direction: str
+    offset: int
+
+    @staticmethod
+    def from_str(s: str) -> "Fold":
+        match = FOLD_RE.match(s)
+        assert match
+        return Fold(match["dir"], int(match["off"]))
+
+
+class Grid:
+    def __init__(self, points: Set[Point]):
+        self.rows = max(y for x, y in points) + 1
+        self.cols = max(x for x, y in points) + 1
+        self.points = points
+
+    def apply_fold(self, fold: Fold):
+        if fold.direction == "y":
+            # Find all points that are below this line
+            below = {(x, y) for x, y in self.points if y > fold.offset}
+            # Find their new positions and then remove the old ones
+            self.points -= below
+            self.points |= {(x, self.rows - y - 1) for (x, y) in below}
+            self.rows //= 2
+        else:
+            # Find all points that are to the right of this line
+            right = {(x, y) for x, y in self.points if x > fold.offset}
+            # Find their new positions and then remove the old ones
+            self.points -= right
+            self.points |= {(self.cols - x - 1, y) for (x, y) in right}
+            self.cols //= 2
+
+    def display(self) -> Sequence[str]:
+        grid = [["." for _ in range(self.cols)] for _ in range(self.rows)]
+        for x, y in self.points:
+            grid[y][x] = "#"
+        return ["".join(line) for line in grid]
+
+
+def part1(grid: Grid, folds: Sequence[Fold]):
+    grid = deepcopy(grid)
+    grid.apply_fold(folds[0])
+    print(len(grid.points))
+
+
+def part2(grid: Grid, folds: Sequence[Fold]):
+    for fold in folds:
+        grid.apply_fold(fold)
+    print("\n".join(grid.display()))
+
+
+points_str, folds_str = sys.stdin.read().split("\n\n")
+points = {
+    (int(a), int(b))
+    for a, b in map(lambda line: line.split(","), points_str.split("\n"))
+}
+
+grid = Grid(points)
+folds = [Fold.from_str(line) for line in folds_str.split("\n")]
+
+print("Part 1")
+part1(grid, folds)
+print("Part 2")
+part2(grid, folds)