Python HeapSort

__author__ = 'student'
print 'hello world hello python'

'''
heap sort
root  leftchild 2n+1 rightchild 2n+2
compare them and get the maxnode
step by step think way
one step write the perfect program is hard
but it is easy to write your think step by step
build max heap
then swap the biggest number with the size
heap sort is a tuning for selection sort.
'''
la =[1,5,7,3,20,0,9,4]
print ', '.join(str(x) for x in la)
#from bottom to top
def heap(la,root,heap_size=None):
    if heap_size is None:
        length=la.__len__()
    else:
        length=heap_size
    lc=root*2+1
    rc=root*2+2
    maxnode=root
    if length>lc and la[lc]>la[root]:
        maxnode=lc
    if length>rc and la[rc]>la[maxnode]:
        maxnode=rc
    if maxnode!=root:
        la[maxnode],la[root]=la[root],la[maxnode]
        heap(la,maxnode,heap_size)

#build max heap
def build_max_heap(la):
    root=la.__len__()/2-1
    while root>=0:
        heap(la,root)
        root-=1
#heap sort
#print ','.join (str(x) for x in xrange(la.__len__(),0,-1))
build_max_heap(la)

def heap_sort(la):
    heap_size=la.__len__()-1
    for i in xrange(heap_size,0,-1):
        la[i],la[0]=la[0],la[i] #swap
        heap(la,0,heap_size)
        heap_size-=1
        print heap_size,la
    print la
heap_sort(la)

感悟：

学算法千万不能背，不能去抄别人的代码。

首先要去理解整个逻辑，找一个小的数据集，自己推算出其过程，

然后根据这个过程来写代码。

否则抄别人的代码，被别人的思路牵着走，最后容易忘记，还得回头学。