Day 12

12.input

@@ -0,0 +1,41 @@
+abcccccaaaccccaacaaccaaaaaaaaaaaaaaaaaaaaccccccccccccccccccccccccccccccccccaaaaaa
+abcccccaaaacccaaaaaccaaaaaaaaaaaaaaaaaaaaacccccccccccccccccccccccccccccccccccaaaa
+abcccccaaaaccaaaaaccccaaaccaaaaaacccacaaaaccccccccccccccccaaaccccccccccccccccaaaa
+abcccccaaacccaaaaaaccccccccaaaaaacccccaaccccccccccccccccccaaaccccccccccccccccaaaa
+abcccccccccccccaaaacccccccaaaaaaaaccccccccccccccccccccccccaaacccccccccccccccaaaaa
+abccccccaacccccaacccccccccaaaaaaaaccccccccccccccccccccccccaaaaccaaacccccccccccccc
+abccccccaacccccccccccccccaaacccaaaacccaacaaccccccccccacaccaaacaajaacccccccccccccc
+abcccaaaaaaaaccccacccccccaaaccccaaacccaaaaaccccccccccaaaaaaajjjjkkkccccccaacccccc
+abcccaaaaaaaacaaaacccccccccccccccccccaaaaaccccccccciiiijjjjjjjjjkkkkcaaaaaacccccc
+abcccccaaaacccaaaaaacccccccccccccccccaaaaaacccccciiiiiijjjjjjjrrrkkkkaaaaaaaacccc
+abcccccaaaaacccaaaacccccccccaacccccccccaaaaccccciiiiiiiijjjjrrrrrsskkaaaaaaaacccc
+abccccaaaaaaccaaaaacccccccccaaaacccccccaccccccciiiiqqqqrrrrrrrrrssskkkaaaaaaacccc
+abaaccaaccaaccaacaacccccccaaaaaaccccccccccccccciiiqqqqqrrrrrrruussskkkaaaaacccccc
+abaaaacccccccccccccccccccccaaaaccccccccaaaccccciiqqqqqttrrrruuuuussskkaaaaacccccc
+abaaaacccccccccccccccccccccaaaaaccccccccaaaaccchiqqqtttttuuuuuuuussskkcccaacccccc
+abaaacccccaaaccacccccccccccaacaaccccccaaaaaaccchhqqqtttttuuuuxxuussslllcccccccccc
+abaaaaccccaaaaaacaaccccccaccccccccccccaaaaacccchhqqqttxxxxuuxxyyusssllllccccccccc
+abacaaccccaaaaaacaaaaaaaaaaccccccccccccaaaaaccchhqqqttxxxxxxxxyuusssslllccccccccc
+abcccccccaaaaaaacaaaaaaaaaccccaacccccccaaccaccchhhqqtttxxxxxxyyvvvsssslllcccccccc
+abcccccccaaaaaaaaaaaaaaaaaccccaaaaccccccccccccchhhppqttxxxxxyyyvvvvsqqqlllccccccc
+SbcccaaccaaaaaaaaaaaaaaaaaacaaaaaacccccccccccchhhhpptttxxxEzzyyyyvvvqqqqlllcccccc
+abcccaaccccaaacaaaaaaaaaaaaacaaaaccccccccccccchhhppptttxxxyyyyyyyyvvvqqqlllcccccc
+abaaaaaaaacaaacaaaaaaaaaaaaacaaaaacaaccccccccchhpppsssxxyyyyyyyyvvvvvqqqlllcccccc
+abaaaaaaaaccccccccaaacaaaccccaacaaaaaccccccaagggpppsswwwwwwyyyvvvvvvqqqmmmmcccccc
+abccaaaaccccaacaacaaacaaacccccccccaaacaaaccaagggppssswwwwwwyyywvvqqqqqqmmmccccccc
+abcaaaaaccccaaaaacaaccaaccaaaccaaaaaaaaaaaaaagggppsssswwwswwyywvrqqqqmmmmcccccccc
+abcaaaaaaccaaaaacccccccccaaaaccaaaaaaaaaacaaagggpppssssssswwwwwwrrqmmmmmccccccccc
+abcaacaaaccaaaaaaccccccccaaaaccccaaaaaacccaaagggppppssssssrwwwwrrrmmmmmdccccccccc
+abccccaaaccaaaaaaccccccccaaaaccccaaaaaacccaacggggpooooooosrrwwwrrnmmmddddcacccccc
+abccccaaaaaaaacccccccccccccccccccaaaaaaaccccccggggoooooooorrrrrrrnnmdddddaaaacccc
+abcccccaaaaaaccccccccccccccccccccaaacaaacccccccggggfffooooorrrrrrnnddddaaaaaacccc
+abccaaaaaaaacccccccccccccccccccccaccccccccccccccggffffffooonrrrrnnndddaaaaaaacccc
+abccaaaaaaaaaccccaacccccccccccccccccccccccccccccccfffffffoonnnnnnndddcaaaaacccccc
+abccaaaaaaaaaacccaaccccccccccccccaccccccccccccccccccccffffnnnnnnnedddaaaaaacccccc
+abcccccaaaaaaaaaaaacccccccaccccaaacccccccccccccccccccccfffeennnneeedcccccaacccccc
+abcccccaaacccaaaaaaaaccccaaacccaaaccacccccccccccccccccccafeeeeeeeeecccccccccccccc
+abcccccaaccccaaaaaaaaacccaaaaaaaaaaaaccccccaaaccccccccccaaeeeeeeeeeccccccccccccca
+abaccccccccccaaaaaaaaacccaaaaaaaaaaacccccccaaaaacccccccaaaaceeeeecccccccccccaccca
+abaccccccccccaaaaaaaaccaaaaaaaaaaaaaacccccaaaaaccccccccaaaccccaaacccccccccccaaaaa
+abaccccccccccaaaaaaacccaaaaaaaaaaaaaacccccaaaaacccccccccccccccccccccccccccccaaaaa
+abaccccccccccaccaaaacccaaaaaaaaaaaaaaccccccaaaaaccccccccccccccccccccccccccccaaaaa

12.py

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+from queue import PriorityQueue
+
+DIRECTIONS = [(0, 1), (0, -1), (1, 0), (-1, 0)]
+
+grid = [[c for c in line.strip()] for line in open("12.input")]
+
+starts = []
+
+for y, line in enumerate(grid):
+    for x, c in enumerate(line):
+        if c == 'S':
+            start = (x, y)
+            grid[y][x] = 'a'
+        elif c == 'E':
+            end = (x, y)
+            grid[y][x] = 'z'
+        elif c == 'a':
+            starts.append((x, y))
+
+size = (len(grid[0]), len(grid))
+
+def nxt(pos):
+    x, y = pos
+    locs = []
+
+    for (dx, dy) in DIRECTIONS:
+        if 0 <= x + dx and x + dx < size[0]:
+            if 0 <= y + dy and y + dy < size[1]:
+                if ord(grid[y + dy][x + dx]) - ord(grid[y][x]) <= 1:
+                    locs.append((x + dx, y + dy))
+
+    return locs
+
+def search(grid, start, end):
+    dists = {}
+    dists[start] = 0
+
+    queue = PriorityQueue()
+    queue.put((0, start))
+
+    while not queue.empty():
+        _, current = queue.get()
+        dist = dists[current]
+        if current == end:
+            return dist
+        for loc in nxt(current):
+            old_dist = dists.get(loc, 1000000)
+            if dist + 1 < old_dist:
+                dists[loc] = dist + 1
+                queue.put((dists[loc], loc))
+
+    return 10000000
+
+# Part 1
+print(search(grid, start, end))
+
+# Part 2, disgusting brute force. Could be done faster by inverting the
+# neighbour condition and searching from 'end' to any of the positions in
+# 'starts'.
+print(min(search(grid, start, end) for start in starts))