networkx

2022/day12.py

@@ -0,0 +1,71 @@
+from string import ascii_lowercase
+import networkx
+
+with open("input.txt") as f:
+    lines = f.read().splitlines()
+
+
+test_lines = """Sabqponm
+abcryxxl
+accszExk
+acctuvwj
+abdefghi""".splitlines()
+
+
+heights = {a: i for i, a in enumerate(ascii_lowercase)}
+heights["S"] = 0
+heights["E"] = 25
+
+
+def find_position(lines, marker):
+    for r, row in enumerate(lines):
+        for c, col in enumerate(row):
+            if col == marker:
+                return r, c
+
+
+def build_graph(lines):
+    graph = networkx.DiGraph()
+    for row, line in enumerate(lines):
+        for col, val in enumerate(line):
+            height = heights[lines[row][col]]
+            neighbors = [
+                (row + 1, col),
+                (row, col + 1),
+                (row - 1, col),
+                (row, col - 1),
+            ]
+            for y, x in neighbors:
+                if y < 0 or x < 0 or y >= len(lines) or x >= len(line):
+                    continue
+                neighbor_height = heights[lines[y][x]]
+                if neighbor_height - height <= 1:
+                    graph.add_edge((row, col), (y, x))
+    return graph
+
+
+def solve(lines):
+    graph = build_graph(lines)
+    start = find_position(lines, "S")
+    end = find_position(lines, "E")
+    shortest = networkx.shortest_path_length(graph, start, end)
+    print("part a:", shortest)
+
+    all_starting_positions = []
+    for row, line in enumerate(lines):
+        for col, val in enumerate(line):
+            if val == "a":
+                all_starting_positions.append((row, col))
+
+    for position in all_starting_positions:
+        try:
+            length = networkx.shortest_path_length(graph, position, end)
+        except:
+            pass
+        if length < shortest:
+            shortest = length
+
+    print("part b:", shortest)
+
+
+solve(lines)