2024 - Day 15A: Warehouse Woes

2024/day15.py

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+import enum
+
+from day_base import Day
+
+
+class Day15(Day):
+
+    class Cell(enum.Enum):
+        FREE = '.'
+        BOX = 'O'
+        WALL = '#'
+
+    def __init__(self):
+        super().__init__(2024, 15, 'Warehouse Woes', debug=True)
+
+    def parse_data(self):
+        grid = []
+        current_location = None
+        i = 0
+        while len(line := self.input[i]) > 0:
+            row = []
+            for j, x in enumerate(line):
+                row.append(self.Cell(x) if x in self.Cell else self.Cell.FREE)
+                if x == '@':
+                    current_location = (i, j)
+            grid.append(row)
+            i += 1
+        instructions = ''.join(self.input[i:])
+
+        return grid, instructions, current_location
+
+    def part_a(self):
+        grid, instructions, current_location = self.parse_data()
+
+        for instruction in instructions:
+            (i, j) = current_location
+            if instruction == '<':
+                (di, dj) = (0, -1)
+                forward = list(reversed(grid[i][:j]))
+            elif instruction == 'v':
+                (di, dj) = (1, 0)
+                forward = [row[j] for row in grid[i + 1:]]
+            elif instruction == '>':
+                (di, dj) = (0, 1)
+                forward = grid[i][j + 1:]
+            else:
+                (di, dj) = (-1, 0)
+                forward = list(reversed([row[j] for row in grid[:i]]))
+            (ti, tj) = (i + di, j + dj)
+
+            # We can just move, easy!
+            if grid[ti][tj] == self.Cell.FREE:
+                current_location = (ti, tj)
+                continue
+
+            # We cannot move through a wall, even easier!
+            elif grid[ti][tj] == self.Cell.WALL:
+                continue
+
+            # We have to move a box, can we tho?
+            if self.Cell.FREE in forward:
+                # Check where is the first wall
+                first_wall = forward.index(self.Cell.WALL)
+
+                # We can still move. Move the current box to the next free location
+                empty_index = forward.index(self.Cell.FREE)
+
+                # We cannot move boxes through a wall, so the free spot should be before the first wall.
+                if empty_index < first_wall:
+                    grid[ti][tj] = self.Cell.FREE
+                    grid[ti + di * empty_index][tj + dj * empty_index] = self.Cell.BOX
+                    current_location = (ti, tj)
+            else:
+                # We cannot move after all.
+                continue
+
+        return sum(100 * i + j for i, row in enumerate(grid) for j, x in enumerate(row) if x == self.Cell.BOX)
+
+
+if __name__ == '__main__':
+    (Day15()).run()
+