day 16, resolve graph bfs

d16/run.py

@@ -0,0 +1,54 @@
+import sys
+from grid import *
+from collections import defaultdict as DD
+from collections import deque
+from math import inf
+
+def BFS(start, end, G):
+    seats = set()
+    seen = DD(lambda:inf)
+    dq = deque()
+    path = set()
+    path.add(start)
+    dq.append((start, (1, 0), 0, path))
+    best = inf
+    while dq:
+        pos, dirn, score, path = dq.popleft()
+        if score > seen[(pos, dirn)] or score > best:
+            continue
+        seen[(pos, dirn)] = score
+        if pos == end:
+            if score < best:
+                best = score
+                seats = path
+            elif score == best:
+                seats.update(path)
+            continue
+        dx, dy = dirn
+        x, y = pos
+        npos = (x+dx, y+dy)
+        if get_in_grid(G,*npos) != '#':  # can move fw
+            np = path.copy()
+            np.add(npos)
+            dq.append((npos, dirn, score+1, np))
+        # turn 90°, both sides
+        ndy = dx
+        ndx = dy
+        np = path.copy()
+        dq.append((pos, (ndx, ndy), score+1000, np))
+        np = path.copy()
+        dq.append((pos, (-ndx, -ndy), score+1000, np))
+    return best, seats
+
+L = sys.stdin.read().strip().split('\n')
+G = [list(l) for l in L]
+start = end = (-1, -1)  # must init with correct type for codon
+for y, row in enumerate(L):
+    for x, v in enumerate(row):
+        if v == 'S':
+            start = (x, y)
+        elif v == 'E':
+            end = (x, y)
+p1, path = BFS(start, end, G)
+score, seats = BFS(start, end, G)
+print(p1, len(path))