Solution to problem 13 in Python

src/Year_2016/P13.py

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+# --- Day 13: A Maze of Twisty Little Cubicles ---
+
+# You arrive at the first floor of this new building to discover a much
+# less welcoming environment than the shiny atrium of the last one.
+# Instead, you are in a maze of twisty little cubicles, all alike.
+
+# Every location in this area is addressed by a pair of non-negative
+# integers (x,y). Each such coordinate is either a wall or an open space.
+# You can't move diagonally. The cube maze starts at 0,0 and seems to
+# extend infinitely toward positive x and y; negative values are invalid,
+# as they represent a location outside the building. You are in a small
+# waiting area at 1,1.
+
+# While it seems chaotic, a nearby morale-boosting poster explains, the
+# layout is actually quite logical. You can determine whether a given x,y
+# coordinate will be a wall or an open space using a simple system:
+
+#     Find x*x + 3*x + 2*x*y + y + y*y.
+#     Add the office designer's favorite number (your puzzle input).
+#     Find the binary representation of that sum; count the number of bits
+#     that are 1.
+#         If the number of bits that are 1 is even, it's an open space.
+#         If the number of bits that are 1 is odd, it's a wall.
+
+# For example, if the office designer's favorite number were 10, drawing
+# walls as # and open spaces as ., the corner of the building containing
+# 0,0 would look like this:
+
+#   0123456789
+# 0 .#.####.##
+# 1 ..#..#...#
+# 2 #....##...
+# 3 ###.#.###.
+# 4 .##..#..#.
+# 5 ..##....#.
+# 6 #...##.###
+
+# Now, suppose you wanted to reach 7,4. The shortest route you could take
+# is marked as O:
+
+#   0123456789
+# 0 .#.####.##
+# 1 .O#..#...#
+# 2 #OOO.##...
+# 3 ###O#.###.
+# 4 .##OO#OO#.
+# 5 ..##OOO.#.
+# 6 #...##.###
+
+# Thus, reaching 7,4 would take a minimum of 11 steps (starting from your
+# current location, 1,1).
+
+# What is the fewest number of steps required for you to reach 31,39?
+
+# Your puzzle input is 1350.
+
+inp = 1350
+destination = (31, 39)
+size = 100
+
+
+def is_wall(x: int, y: int) -> bool:
+    res = inp + (x * x + 3 * x + 2 * x * y + y + y * y)
+    return format(res, "b").count("1") % 2
+
+
+def part_1() -> None:
+    visited = {(1, 1)}
+    steps = 0
+
+    while visited:
+        places_to_check = visited.copy()
+        visited = set()
+        for dx, dy in places_to_check:
+            # neighboring points to the current point (left, right, up, and down)
+            for x, y in [
+                (dx + 1, dy),
+                (dx - 1, dy),
+                (dx, dy + 1),
+                (dx, dy - 1),
+            ]:
+                if x < 0 or y < 0 or (x, y) in visited or is_wall(x, y):
+                    continue
+                visited.add((x, y))
+        steps += 1
+
+        if destination in visited:
+            print(steps)
+            break
+
+
+# --- Part Two ---
+
+# How many locations (distinct x,y coordinates, including
+# your starting location) can you reach in at most 50 steps?
+
+
+def part_2() -> None:
+    visited = traversed = {(1, 1)}
+    steps = 0
+
+    while visited:
+        places_to_check = visited.copy()
+        visited = set()
+        for dx, dy in places_to_check:
+            # neighboring points to the current point (left, right, up, and down)
+            for x, y in [
+                (dx + 1, dy),
+                (dx - 1, dy),
+                (dx, dy + 1),
+                (dx, dy - 1),
+            ]:
+                if x < 0 or y < 0 or (x, y) in visited or is_wall(x, y):
+                    continue
+                visited.add((x, y))
+                traversed.add((x, y))
+        steps += 1
+
+        if steps == 50:
+            print(len(traversed))
+            break
+
+
+if __name__ == "__main__":
+    part_1()
+    part_2()