Why doesn't my heapify work?

[Dongsheng Ruan]

I want to turn an Array into a heap, but my code just doesn't work: no
change after execution.

A=[3,5,4,9,6,7]
m=len(A)-1



for i in range(m,1):
t=(i-1)/2
if A>A[t]:
A,A[t]=A[t],A

 

[Diez B. Roggisch]

I want to turn an Array into a heap, but my code just doesn't work: no
change after execution.

A=[3,5,4,9,6,7]
m=len(A)-1



for i in range(m,1):
t=(i-1)/2
if A>A[t]:
A,A[t]=A[t],A

First of all, there is the module heapq that will just do it.

And then you seem to misunderstand how the range-function works. range(m, 1)
will always be the empty list. See

pydoc range

for how it operates.

Overall, your code is very unpythonic, to say the least. I suggest you start
reading the python tutorial first:

http://docs.python.org/tut/

Especially the looping techniques section:

http://docs.python.org/tut/node7.html#SECTION007600000000000000000

Diez

 

[Ruan]

Can't range go from larger to smaller?

I want to turn an Array into a heap, but my code just doesn't work: no
change after execution.

A=[3,5,4,9,6,7]
m=len(A)-1



for i in range(m,1):
t=(i-1)/2
if A>A[t]:
A,A[t]=A[t],A

First of all, there is the module heapq that will just do it.

And then you seem to misunderstand how the range-function works. range(m,
1)
will always be the empty list. See

pydoc range

for how it operates.

Overall, your code is very unpythonic, to say the least. I suggest you
start
reading the python tutorial first:

http://docs.python.org/tut/

Especially the looping techniques section:

http://docs.python.org/tut/node7.html#SECTION007600000000000000000

Diez

 

[Ruan]

I found out what is wrong.

You must give it a negative step, like range(10,1,-1)

But my code is not good enought for heapify.

I will try again.

Can't range go from larger to smaller?

I want to turn an Array into a heap, but my code just doesn't work: no
change after execution.

A=[3,5,4,9,6,7]
m=len(A)-1



for i in range(m,1):
t=(i-1)/2
if A>A[t]:
A,A[t]=A[t],A

First of all, there is the module heapq that will just do it.

And then you seem to misunderstand how the range-function works. range(m,
1)
will always be the empty list. See

pydoc range

for how it operates.

Overall, your code is very unpythonic, to say the least. I suggest you
start
reading the python tutorial first:

http://docs.python.org/tut/

Especially the looping techniques section:

http://docs.python.org/tut/node7.html#SECTION007600000000000000000

Diez

 

[skip]

ruan> Can't range go from larger to smaller?

Yes. Read the doc:

range(...)
range([start,] stop[, step]) -> list of integers

Return a list containing an arithmetic progression of integers.
range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
When step is given, it specifies the increment (or decrement).
For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
These are exactly the valid indices for a list of 4 elements.

To go from larger to smaller you need a negative step size. Also, note that
the endpoint is never included. range(10) serves up 0 throu 9.

Skip

 

[=?ISO-8859-1?Q?BJ=F6rn_Lindqvist?=]

You do know about the heapq module?
http://docs.python.org/dev/lib/module-heapq.html