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47 lines
832 B
Ruby
47 lines
832 B
Ruby
# Max-oriented Priority Queue based on the binary heap,
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# it requires ~lgN compares for insert and ~2lg N compares for remove the maximum,
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# see test/priority_queue_test.rb
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class PriorityQueue
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def initialize
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@pq = [nil]
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end
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def insert(key)
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@pq << key
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swim(@pq.length - 1)
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end
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def delete_max
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return nil if length == 0
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return @pq.pop if length == 1
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max = @pq[1]
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@pq[1] = @pq.pop
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sink(1)
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max
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end
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def length
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@pq.length - 1
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end
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private
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def swim(k)
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while (k > 1) && (@pq[k/2] < @pq[k])
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@pq[k/2], @pq[k] = @pq[k], @pq[k/2]
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k /= 2
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end
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end
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def sink(k)
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while (2*k <= length)
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j = 2*k
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j += 1 if (j < length) && (@pq[j] < @pq[j + 1])
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break if @pq[k] >= @pq[j]
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@pq[k], @pq[j] = @pq[j], @pq[k]
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k = j
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end
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end
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end
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