32 lines
1,015 B
Python
32 lines
1,015 B
Python
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def queens_lex(n):
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a = list(range(n))
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up = [True]*(2*n - 1)
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down = [True]*(2*n - 1)
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def sub(i):
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if i == n:
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yield tuple(a)
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else:
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for k in range(i, n):
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a[i], a[k] = a[k], a[i]
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j = a[i]
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p = i + j
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q = i - j + n - 1
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if up[p] and down[q]:
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up[p] = down[q] = False
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yield from sub(i + 1)
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up[p] = down[q] = True
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x = a[i]
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for k in range(i + 1, n):
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a[k - 1] = a[k]
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a[n - 1] = x
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yield from sub(0)
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next(queens(31))
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(0, 2, 4, 1, 3, 8, 10, 12, 14, 6, 17, 21, 26, 28, 25, 27, 24, 30, 7, 5, 29, 15, 13, 11, 9, 18, 22, 19, 23, 16, 20)
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next(queens_lex(31))
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(0, 2, 4, 1, 3, 8, 10, 12, 14, 5, 17, 22, 25, 27, 30, 24, 26, 29, 6, 16, 28, 13, 9, 7, 19, 11, 15, 18, 21, 23, 20)
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#Compare to A065188
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#1, 3, 5, 2, 4, 9, 11, 13, 15, 6, 8, 19, 7, 22, 10, 25, 27, 29, 31, 12, 14, 35, 37, ...
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