[wip] 2024 day 15

2024/day15/day15.py

@@ -0,0 +1,99 @@
+DIRECTIONS = {
+    "^": 0 - 1j,  # up
+    ">": 1 + 0j,  # right
+    "v": 0 + 1j,  # down
+    "<": -1 + 0j,  # left
+}
+
+
+def find_start_pos(grid):
+    for y, row in enumerate(grid):
+        for x, _ in enumerate(row):
+            if grid[y][x] == "@":
+                return complex(x, y)
+
+
+def get_pos(grid, pos):
+    x, y = int(pos.real), int(pos.imag)
+    if 0 <= x < len(grid[0]) and 0 <= y < len(grid):
+        return grid[y][x]
+    return None
+
+
+def set_pos(grid, pos, val):
+    x, y = int(pos.real), int(pos.imag)
+    grid[y][x] = val
+
+
+def debug_print(grid, move):
+    print("Move ", move)
+    for row in grid:
+        print("".join(row))
+
+
+def push(grid, pos, movement):
+    direction = DIRECTIONS[movement]
+    start_pos = pos + direction
+    # Find the end pos of a consecutive "O" chain
+    end_pos = start_pos
+    while get_pos(grid, end_pos + direction) == "O":
+        end_pos += direction
+    if get_pos(grid, end_pos + direction) == ".":
+        if movement == ">":
+            start_x, end_x = int(start_pos.real), int(end_pos.real)
+            y = int(start_pos.imag)
+            for i in range(end_x, start_x - 1, -1):
+                grid[y][i+1] = "O"  # shift "O" to the right
+            grid[y][start_x] = "."
+        elif movement == "<":
+            start_x, end_x = int(start_pos.real), int(end_pos.real)
+            y = int(start_pos.imag)
+            for i in range(start_x, end_x + 1):
+                grid[y][i+1] = "O"  # shift "O" to the left
+            grid[y][start_x] = "."
+        elif movement == "v":
+            start_y, end_y = int(start_pos.imag), int(end_pos.imag)
+            x = int(start_pos.real)
+            for i in range(start_y, end_y + 1):
+                grid[i+1][x] = "O"  # shift "O" down
+            grid[start_y][x] = "."
+        elif movement == "^":
+            start_y, end_y = int(start_pos.imag), int(end_pos.imag)
+            x = int(start_pos.real)
+            for i in range(end_y, start_y - 1, -1):
+                grid[i+1][x] = "O"  # shift "O" up
+            grid[start_y][x] = "."
+
+
+def main(content):
+    grid, movements = content.split("\n\n")
+    grid = [list(x) for x in grid.split("\n")]
+    movements = movements.replace("\n", "")
+    pos = find_start_pos(grid)
+
+    for movement in movements:
+        new_pos = pos + DIRECTIONS[movement]
+        v = get_pos(grid, new_pos)
+        match v:
+            case ".":
+                set_pos(grid, pos, ".")
+                set_pos(grid, new_pos, "@")
+                pos = new_pos
+            case "O": 
+                push(grid, pos, movement)
+                if get_pos(grid, new_pos) == ".":
+                    set_pos(grid, new_pos, "@")
+                    set_pos(grid, pos, ".")
+                    pos = new_pos
+            case "#": pass
+            case c: raise RuntimeError("This should never happen", c)
+        debug_print(grid, movement)
+
+
+if __name__ == "__main__":
+    import sys
+    infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
+    with open(infile) as f:
+        content = f.read()
+        main(content)
+