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- #!/usr/bin/env python3
- import sys
- class TuringMachine:
- def __init__(self, f):
- def last_word(linenr):
- return lines[linenr].split()[-1][:-1]
- def state_index(state):
- return (ord(state) - ord('A')) * 2
- def transition(start):
- write_val = int(last_word(start))
- move = 1 if last_word(start + 1) == 'left' else -1
- next_state = state_index(last_word(start + 2))
- return write_val, move, next_state
- lines = f.read().split('\n')
- self.state = state_index(last_word(0))
- self.steps = int(lines[1].split()[-2])
- self.trans = []
- self.tape = 0
- self.index = 0
- for start in range(3, len(lines), 10):
- in_state = state_index(last_word(start))
- assert in_state == len(self.trans)
- self.trans.append(transition(start + 2))
- self.trans.append(transition(start + 6))
- def step(self):
- read_val = (self.tape >> self.index) & 1
- write_val, move, next_state = self.trans[self.state + read_val]
- if write_val != read_val:
- mask = 1 << self.index
- if write_val:
- self.tape |= mask
- else:
- self.tape &= ~mask
- self.index += move
- if self.index == -1:
- self.tape <<= 1
- self.index = 0
- self.state = next_state
- self.steps -= 1
- def diag(self):
- while self.steps > 0:
- self.step()
- checksum = 0
- tape = self.tape
- while tape > 0:
- checksum += tape & 1
- tape >>= 1
- return checksum
- print(TuringMachine(sys.stdin).diag())
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