54 lines
1.2 KiB
Python
54 lines
1.2 KiB
Python
import sys
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input = sys.stdin.readline
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def check(U):
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for i in U:
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for j in i:
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if j == 0:
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return False
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return True
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def solve(M, N, U, ir):
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step = 0
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delta = (
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(-1, 0),
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(1, 0),
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(0, -1),
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(0, 1),
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)
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rotten = [ir]
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while not check(U):
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rotten.append([])
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for r in rotten[step]:
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for dm, dn in delta:
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new = r[0] + dm, r[1] + dn
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if 0 <= new[0] < M and 0 <= new[1] < N:
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if U[new[1]][new[0]] != 0:
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continue
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else:
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U[new[1]][new[0]] = 1
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rotten[step + 1].append(new)
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if rotten[-1]:
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step += 1
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else:
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return -1
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return step
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if __name__ == "__main__":
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M, N = map(int, input().split())
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U = [[None for _ in range(M)] for _ in range(N)] # U[h][n][m]
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init_rottens = []
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for n in range(N):
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for m, v in enumerate(map(int, input().split())):
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U[n][m] = v
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if v == 1:
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init_rottens.append((m, n))
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print(solve(M, N, U, init_rottens))
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