25 lines
577 B
Python
25 lines
577 B
Python
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#!/usr/bin/env python3
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from fractions import Fraction
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def cut(state, i):
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return state[:i] + (state[i]-1,) + \
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tuple(n + 1 for n in state[i+1:])
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def search(state=(1, 0, 0, 0, 0), cache={}):
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if state in cache:
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return cache[state]
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if sum(state) == state[-1] == 1:
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return 1
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r = 0
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for i, p in enumerate(state):
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if not p:
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continue
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r += Fraction(p, sum(state)) * \
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search(cut(state, i), cache)
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r += (sum(state) == 1)
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cache[state] = r
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return r
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print(float(round(search(), 6) - 2))
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