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