2022 day 12

2022/12/part2

@@ -0,0 +1,68 @@
+#!/usr/bin/env python
+
+import math
+from collections import defaultdict
+
+MAP = []
+END = (0, 0)
+
+def possible(x, y):
+    global MAP
+
+    threshold = MAP[y][x] + 1 # Can't go higher than this, can always go lower
+    points = [(x-1,y),(x+1,y),(x,y-1),(x,y+1)]
+
+    out = []
+    for (x,y) in points:
+        if x < 0 or y < 0:
+            continue
+        if len(MAP) < y+1 or len(MAP[y]) < x+1:
+            continue
+        if MAP[y][x] > threshold:
+            continue
+        out.append((x,y))
+    return out
+
+with open('input') as f:
+    for y, line in enumerate(f):
+        row = []
+        for x, byte in enumerate(line.rstrip()):
+            if byte == 'S':
+                byte = 'a'
+            elif byte == 'E':
+                byte = 'z'
+                END = (x,y)
+            row.append(ord(byte) - ord('a'))
+        MAP.append(row)
+
+def search(start):
+    distances = defaultdict(lambda: math.inf)
+    distances[start] = 0
+    visited = set([])
+    queue = [start]
+
+    while len(queue) > 0:
+        pos = queue.pop(0)
+        visited.add(pos)
+
+        for neighbour in possible(*pos):
+            if neighbour == END:
+                return distances[pos] + 1
+
+            if distances[neighbour] > distances[pos] + 1:
+                distances[neighbour] = distances[pos] + 1
+
+            if neighbour not in visited and neighbour not in queue:
+                queue.append(neighbour)
+
+    return None # Some start positions may not have a valid path
+
+results = []
+for y, row in enumerate(MAP):
+    for x, height in enumerate(row):
+        if height == 0:
+            result = search((x,y))
+            if result != None:
+                results.append(result)
+
+print(sorted(results)[0])