[2022][day 12] adding solution

2022/AOC12.py

@@ -0,0 +1,80 @@
+"""
+A personal best: 00:09:16 (rank 179) for part 1, 00:12:42 (rank 225) for part 2.
+Reused existing code from 2021 day 15.
+"""
+
+import heapq
+from typing import List, Tuple, Set
+
+from _utils import read_input, timer, Solution, GridDict, Point
+
+
+def process_input(filename: str):
+ _input = read_input(filename)
+ grid = {}
+ for x, line in enumerate(_input):
+ for y, char in enumerate(line):
+ if char == "S":
+ start = x, y
+ elevation = ord("a")
+ elif char == "E":
+ end = x, y
+ elevation = ord("z")
+ else:
+ elevation = ord(char)
+
+ grid[(x, y)] = elevation - ord("a")
+
+ return start, end, grid
+
+
+def get_neighbors(grid: GridDict, pos: Point) -> List[Point]:
+ """
+ Returns neighbors of a tile if only allowed movements
+ are up, left, right, down (no diagonals).
+ """
+ x, y = pos
+ neighbors = [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)]
+ neighbors = [n for n in neighbors if n in grid]
+ return neighbors
+
+
+def least_risky_path(grid: GridDict, start: Point, end: Point) -> int:
+ """
+ Returns shortest path to destination. Djikstra algorithm.
+ """
+ queue = []
+ heapq.heappush(queue, (0, start))
+ visited = set()
+
+ while queue:
+ steps, current_node = heapq.heappop(queue)
+ elevation = grid[current_node]
+
+ if current_node == end:
+ return steps
+ elif current_node not in visited:
+ visited.add(current_node)
+
+ neighbors = get_neighbors(grid, current_node)
+ for next_node in neighbors:
+ if next_node not in visited and grid[next_node] <= elevation + 1:
+ heapq.heappush(queue, (steps + 1, next_node))
+
+ return -1
+
+
+@timer
+def main(filename: str) -> Solution:
+ start, end, grid = process_input(filename)
+ part_1_solution = least_risky_path(grid, start, end)
+ starts = {k for k, v in grid.items() if v == 0}
+ steps = [least_risky_path(grid, s, end) for s in starts]
+ part_2_solution = min([s for s in steps if s > 0])
+ return part_1_solution, part_2_solution
+
+
+if __name__ == "__main__":
+ part_1_solution, part_2_solution = main("aoc12.txt")
+ print(f"PART 1: {part_1_solution}") # 468
+ print(f"PART 2: {part_2_solution}") # 459

2022/aoc12.txt

@@ -0,0 +1,41 @@
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