#!/usr/bin/ruby1.8
def partitions(set)
yield [] if set.empty?
(0 ... 2 ** set.size / 2).each do |i|
parts = [[], []]
set.each do |item|
parts[i & 1] << item
i >>= 1
end
partitions(parts[1]) do |b|
result = [parts[0]] + b
result = result.reject do |e|
e.empty?
end
yield result
end
end
end
partitions([1, 2, 3, 4]) do |e|
p e
end
# => [[1, 2, 3, 4]]
# => [[2, 3, 4], [1]]
# => [[1, 3, 4], [2]]
# => [[3, 4], [1, 2]]
# => [[3, 4], [2], [1]]
# => [[1, 2, 4], [3]]
# => [[2, 4], [1, 3]]
# => [[2, 4], [3], [1]]
# => [[1, 4], [2, 3]]
# => [[1, 4], [3], [2]]
# => [[4], [1, 2, 3]]
# => [[4], [2, 3], [1]]
# => [[4], [1, 3], [2]]
# => [[4], [3], [1, 2]]
# => [[4], [3], [2], [1]]
有什么不同：
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