116 lines
2.3 KiB
Python
116 lines
2.3 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 c == '<' and not j < x: continue
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if c == '>' and not j > x: continue
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if c == '^' and not i < y: continue
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if c == 'v' and not i > y: continue
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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] == '.':
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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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dist[x,y] = n
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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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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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print(G)
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def topo(G, start):
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t = []
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seen = set()
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tmp = set()
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def visit(n):
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if n in seen:
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return
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if n in tmp:
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raise Exception("cycle with %s %s" % (repr(n),tmp))
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tmp.add(n)
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for _, p in G[n]:
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visit(p)
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tmp.remove(n)
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seen.add(n)
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t.append(n)
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visit(start)
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t.reverse()
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return t
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print("topo=",topo(G,start))
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dist = {n:float('inf') for n in G}
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pred = {}
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dist[start] = 0
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T = topo(G, start)
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for u in T:
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for n,v in G[u]:
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w = -n
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if dist[v] > dist[u] + w:
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dist[v] = dist[u] + w
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pred[v] = u
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print(dist)
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print(-min(dist.values()))
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#import astar
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#def goal(state):
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# x,y = state
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# return y == len(map)-1
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#
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#M = max(n for p in G for n,_ in G[p])
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#
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#def nb(state):
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# p = state
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# for n,q in G[p]:
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# yield 1+M-n, q
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#
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#n, g, path = astar.search(start, goal, nb)
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#print(g,path)
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#t = 0
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#for p, q in zip(path, path[1:]):
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# t += sum(n for n,r in G[p] if r == q)
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#
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#print(t)
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