85 lines
1.7 KiB
Python
85 lines
1.7 KiB
Python
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import sys
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input = sys.stdin
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map = []
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for line in input:
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map.append(list(line.strip()))
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# construct a graph
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for i,c in enumerate(map[0]):
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if c == '.':
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start = (i,0)
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break
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def neighbors(x,y):
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n = []
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c = map[y][x]
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for i,j in [(y-1,x),(y+1,x),(y,x-1),(y,x+1)]:
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if 0 <= i < len(map) and 0 <= j < len(map[i]):
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if map[i][j] != '#':
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n.append((j,i))
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return n
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spots = []
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for i in range(len(map)):
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for j in range(len(map[i])):
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if map[i][j] in '.<>v^':
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n = neighbors(j,i)
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if len(n) not in (0,2):
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spots.append((j,i))
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def reachable(start,spots):
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q = [(0,start)]
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dist = {}
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r = []
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while q:
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q.sort()
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n,(x,y) = q.pop(0)
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if (x,y) in dist:
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continue
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#print(x,y,neighbors(x,y))
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if (x,y) in spots and (x,y) != start:
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r.append((n,(x,y)))
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else:
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dist[x,y] = n
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for j,i in neighbors(x,y):
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if (j,i) not in dist:
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q.append((n+1,(j,i)))
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return r
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G = {}
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for p in spots:
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G[p] = reachable(p,spots)
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from pprint import pprint
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pprint(G)
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for p in G:
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if p[1] == len(map)-1:
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goal = p
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print("start=",start)
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print("goal=",goal)
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print("brute force...")
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def longest(p, seen, depth):
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best = -10000000
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b = []
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if p == goal:
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return 0,[]
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if p in seen:
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raise Error("alredy seen")
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seen.add(p)
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for n,q in G[p]:
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if q not in seen:
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t,path = longest(q, seen, depth+1)
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if t+n > best:
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best = t+n
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b = [q]+path
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seen.remove(p)
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return best, b
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print(longest(start,set(),0))
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