Add day 12.

2022/day12.py

@@ -0,0 +1,131 @@
+# -*- encoding: utf-8 -*-
+
+import heapq
+import sys
+
+
+def dijkstra(
+    start: tuple[int, int], end: tuple[int, int], grid: list[list[int]]
+) -> list[tuple[int, int]] | None:
+    n_rows = len(grid)
+    n_cols = len(grid[0])
+
+    def heuristic(row: int, col: int) -> int:
+        return abs(end[0] - row) + abs(end[1] - col)
+
+    queue: list[tuple[tuple[int, int], tuple[int, int]]] = []
+    visited: set[tuple[int, int]] = set()
+    lengths: dict[tuple[int, int], int] = {}
+    parents: dict[tuple[int, int], tuple[int, int]] = {}
+
+    heapq.heappush(queue, ((heuristic(start[0], start[1]), 0), start))
+
+    while queue:
+        (_, length), (c_row, c_col) = heapq.heappop(queue)
+
+        visited.add((c_row, c_col))
+
+        if (c_row, c_col) == end:
+            break
+
+        for n_row, n_col in (
+            (c_row - 1, c_col),
+            (c_row + 1, c_col),
+            (c_row, c_col - 1),
+            (c_row, c_col + 1),
+        ):
+
+            if not (n_row >= 0 and n_row < n_rows and n_col >= 0 and n_col < n_cols):
+                continue
+
+            if (n_row, n_col) in visited:
+                continue
+
+            if grid[n_row][n_col] > grid[c_row][c_col] + 1:
+                continue
+
+            if length + 1 < lengths.get((n_row, n_col), n_rows * n_cols):
+                lengths[n_row, n_col] = length + 1
+                parents[n_row, n_col] = (c_row, c_col)
+
+                heapq.heappush(
+                    queue,
+                    (
+                        (heuristic(n_row, n_col) + length + 1, length + 1),
+                        (n_row, n_col),
+                    ),
+                )
+
+    if end not in visited:
+        return None
+
+    path: list[tuple[int, int]] = [end]
+
+    while path[-1] != start:
+        path.append(parents[path[-1]])
+
+    return list(reversed(path))
+
+
+def print_path(path: list[tuple[int, int]], n_rows: int, n_cols: int) -> None:
+    _, end = path[0], path[-1]
+
+    graph = [["." for _c in range(n_cols)] for _r in range(n_rows)]
+    graph[end[0]][end[1]] = "E"
+
+    for i in range(0, len(path) - 1):
+        cr, cc = path[i]
+        nr, nc = path[i + 1]
+
+        if cr == nr and nc == cc - 1:
+            graph[cr][cc] = "<"
+        elif cr == nr and nc == cc + 1:
+            graph[cr][cc] = ">"
+        elif cr == nr - 1 and nc == cc:
+            graph[cr][cc] = "v"
+        elif cr == nr + 1 and nc == cc:
+            graph[cr][cc] = "^"
+        else:
+            assert False, "{} -> {} infeasible".format(path[i], path[i + 1])
+
+    print("\n".join("".join(row) for row in graph))
+
+
+lines = sys.stdin.read().splitlines()
+
+grid = [[ord(cell) - ord("a") for cell in line] for line in lines]
+
+start: tuple[int, int]
+end: tuple[int, int]
+
+# for part 2
+start_s: list[tuple[int, int]] = []
+
+for i_row, row in enumerate(grid):
+    for i_col, col in enumerate(row):
+        if chr(col + ord("a")) == "S":
+            start = (i_row, i_col)
+            start_s.append(start)
+        elif chr(col + ord("a")) == "E":
+            end = (i_row, i_col)
+        elif col == 0:
+            start_s.append((i_row, i_col))
+
+# fix values
+grid[start[0]][start[1]] = 0
+grid[end[0]][end[1]] = ord("z") - ord("a")
+
+path = dijkstra(start, end, grid)
+assert path is not None
+
+print_path(path, n_rows=len(grid), n_cols=len(grid[0]))
+
+answer_1 = len(path) - 1
+print(f"answer 1 is {answer_1}")
+
+answer_2 = min(
+    len(path) - 1
+    for start in start_s
+    if (path := dijkstra(start, end, grid)) is not None
+)
+print(f"answer 2 is {answer_2}")

2022/inputs/day12.txt

@@ -0,0 +1,41 @@
+abcccccccaaaaaaaaccccccccccaaaaaaccccccaccaaaaaaaccccccaacccccccccaaaaaaaaaaccccccccccccccccccccccccccccccccaaaaa
+abcccccccaaaaaaaaacccccccccaaaaaacccccaaacaaaaaaaaaaaccaacccccccccccaaaaaaccccccccccccccccccccccccccccccccccaaaaa
+abcccccccaaaaaaaaaaccccccccaaaaaacaaacaaaaaaaaaaaaaaaaaaccccccccccccaaaaaaccccccccccccccaaacccccccccccccccccaaaaa
+abaaacccccccaaaaaaacccccccccaaacccaaaaaaaaaaaaaaaaaaaaaaaaacccccccccaaaaaaccccccccccccccaaacccccccccccccccccaaaaa
+abaaaaccccccaaaccccccccccccccccccccaaaaaaaaacaaaacacaaaaaacccccccccaaaaaaaacccccccccccccaaaaccaaacccccccccccaccaa
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+abccccaaaaaaaaccccccccccccccccaaccccaacaaaaaaaaaaaaaaccaaaaccccaaacccccccccccccccccccccccccccccccccccccccccaaaaaa