Solve Day 12

Author: destinationunknown

day12/day12.py

@@ -0,0 +1,87 @@
+data = open("input.txt", "r").read().strip().split("\n")
+
+import sys
+from collections import deque
+
+sys.setrecursionlimit(100000000)
+
+UP = (-1, 0)
+DOWN = (1, 0)
+LEFT = (0, -1)
+RIGHT = (0, 1)
+directions = [UP, DOWN, LEFT, RIGHT]
+
+
+def add_pair(a, b):
+    return (a[0] + b[0], a[1] + b[1])
+
+
+def in_grid(pos, grid):
+    row, col = pos
+    return 0 <= row < len(grid) and 0 <= col < len(grid[row])
+
+
+def to_int(x):
+    if x == "S":
+        x = "a"
+    elif x == "E":
+        x = "z"
+    return ord(x) - 96
+
+
+def can_move(a, b, grid):
+    a_r, a_c = a
+    b_r, b_c = b
+    a = to_int(grid[a_r][a_c])
+    b = to_int(grid[b_r][b_c])
+
+    return b - a <= 1
+
+
+def get_neighbours(pos, grid):
+    neighbours = [
+        add_pair(pos, d) for d in directions if in_grid(add_pair(pos, d), grid)
+    ]
+    neighbours = [x for x in neighbours if can_move(pos, x, grid)]
+    return neighbours
+
+
+def bfs(starts, grid):
+    seen = set()
+    q = deque([(start, 0) for start in starts])
+    while q:
+        pos, d = q.popleft()
+        if grid[pos[0]][pos[1]] == "E":
+            return d
+        elif pos in seen:
+            continue
+        else:
+            seen.add(pos)
+            for neighbour in get_neighbours(pos, grid):
+                q.append((neighbour, d + 1))
+
+
+def part_one(data: list[str]):
+    grid = [[*line] for line in data]
+
+    for r in range(len(data)):
+        for c in range(len(data[r])):
+            if grid[r][c] == "S":
+                return bfs([(r, c)], grid)
+
+
+def part_two(data: list[str]):
+    grid = [[*line] for line in data]
+
+    s = []
+    for r in range(len(data)):
+        for c in range(len(data[r])):
+            if grid[r][c] == "S" or grid[r][c] == "a":
+                s.append((r, c))
+
+    return bfs(s, grid)
+
+
+if __name__ == "__main__":
+    print(part_one(data))
+    print(part_two(data))