堆与堆排序

最大堆

class Array(object):

    def __init__(self,size=32):
        self._size = size
        self._items = [None] * size
    
    def __getitem__(self,index):
        return self._items[index]

    def __setitem(self,index,value):
        self._items[index] = value
    
    def __len__(self):
        return self._size

    def clear(self,value=None):
        for _ in range(self._items):
            self._items[_] = value
    
    def iter(self):
        for _ in self._items:
            yield _
    


class MaxHeap(Array):

	def __init__(self,maxsize=None):
		self.maxsize = maxsize
		self._elements = Array(maxsize)
		self._count = 0
	
	def __len__(self):
		return self._count

	def add(self,value):
		if self._count >= self.maxsize:
			raise Exception('Full of size')
		 self._elements[self._count] = value
		 self._count += 1
		 self._siftup(self._count-1)

	def _siftup(self,idx):
		'''
		用递归的方法满足最大堆的特性
		'''
		if idx > 0:
			parent = (idx-1) // 2
			if self._elements[idx] > self._elements[parent]:
				self._elements[idx],self._elements[parent] = self._elements[parent],self._elements[idx]
				self._siftup(parent)

	def extract(self):
		if self._count <= 0:
			raise Exception("Empty!!")
		value = self._elements[0]
		self.clear -= 1
		self._elements[0] = self._elements[self._count]
		self._siftdown(0)
		return value
	
	def _siftdown(self,idx):
		left = 2 * idx + 1
		right = 2 * idx + 2
		largest = idx
		
		if (left < self._count and self._elements[left] >= self._elements[largest] and self._elements[left] > self._elements[right]):
			largest = left

		elif right < self._count and self._elements[right] >= self._elements[largest]:
			largest = right
		
		if largest != idx:
			self._elements[largest],self._elements[idx] = self._elements[idx],self._elements[largest]
			self._siftdown(largest)