42 lines
631 B
Ruby
42 lines
631 B
Ruby
# Sink-based Heapsort algorithm,
|
|
# uses fewer than 2N lg N + 2N compares,
|
|
# see test/heap_sort_test.rb
|
|
class Heap
|
|
def initialize(array)
|
|
@pq = array
|
|
n = @pq.length
|
|
(n / 2).downto(1) { |k| sink(k, n) }
|
|
end
|
|
|
|
def sort
|
|
n = @pq.length
|
|
while n > 1
|
|
exch(1, n)
|
|
n -= 1
|
|
sink(1, n)
|
|
end
|
|
|
|
@pq
|
|
end
|
|
|
|
private
|
|
|
|
def sink(k, n)
|
|
while 2*k <= n
|
|
i = 2*k
|
|
i += 1 if (i < n) && less(i, i + 1)
|
|
break if !less(k, i)
|
|
exch(k, i)
|
|
k = i
|
|
end
|
|
end
|
|
|
|
def exch(i, j)
|
|
@pq[i-1], @pq[j-1] = @pq[j-1], @pq[i-1]
|
|
end
|
|
|
|
def less(i, j)
|
|
@pq[i-1] < @pq[j-1]
|
|
end
|
|
end
|