473,554 Members | 3,055 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

MergeSort

Hi,

the following code is adopted PseudoCode from Introduction to
Algorithms (Cormen et al). For some reason it can't get it to work. I
always get a index of out bounds exception or some weird result.
Secondly I'd like to know how to write this more pythonic. TIA.

import random
import listutil
import unittest

def merge(A, p, q, r):
L = A[p:q]
R = A[q+1:r]
L.append(1001)
R.append(1001)

i=0
j=0
k=p
for k in range(r-p+1):

if L[i] <= R[j]:
A[k] = L[i]
i +=1
else:
A[k] = R[j]
j +=1

def mergeSort(A,p,r ):
if p < r:
q=(p+r)/2
mergeSort(A,p,q )
mergeSort(A,q+1 ,r)
merge(A,p,q,r)

Aug 9 '06 #1
1 2234
On Wed, 09 Aug 2006 12:50:11 -0700, ben81 wrote:
Hi,

the following code is adopted PseudoCode from Introduction to
Algorithms (Cormen et al).
I'm assuming you are doing this as a learning exercise, because -- trust
me on this -- nothing you write in pure Python code will come within cooee
of the speed of Python's build-in sort method.
For some reason it can't get it to work. I
always get a index of out bounds exception or some weird result.
No, don't tell us what the weird result is. I love to guess!

Is it this?

ImportError: No module named listutil
Not that it matters, because listutil doesn't seem to be used in your code.

Secondly I'd like to know how to write this more pythonic. TIA.
Document your code. Don't assume the reader will remember all the
details of Merge Sort. I certainly don't. It will also help you understand
how the algorithm works, which then will help you see what your code is
doing that it shouldn't (such as trying to merge empty lists).

Why are you appending 1001 to both sub-lists?
--
Steven D'Aprano

Aug 10 '06 #2

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

1
3631
by: Jochus | last post by:
Today, I've programmed Mergesort. And it works very good :-)! But now, the teacher said that you could use Mergesort to count the amount of inversions. This is what I found on the internet: --- Note: Merge Sort can be slightly modified to count inversion index (i.e. bubble sort swaps) in O(n log n) time. When the right partition goes in
1
3371
by: Jamal | last post by:
I am working on binary files of struct ACTIONS I have a recursive qsort/mergesort hybrid that 1) i'm not a 100% sure works correctly 2) would like to convert to iteration Any comments or suggestion for improvements or conversion to iteration would be much appreciated
6
2864
by: Jamal | last post by:
I am working on binary files of struct ACTIONS I have a recursive qsort/mergesort hybrid that 1) i'm not a 100% sure works correctly 2) would like to convert to iteration Any comments or suggestion for improvements or conversion to iteration would be much appreciated
2
3554
by: rkk | last post by:
Hi, My mergesort program is below. There is a small piece of logical error/bug in this code which I can't figure out, as a result the output array isn't completely sorted. Requesting your help to resolve this problem. Thanks in advance. #include <stdlib.h> #include <string.h> #include <stdio.h>
51
8592
by: Joerg Schoen | last post by:
Hi folks! Everyone knows how to sort arrays (e. g. quicksort, heapsort etc.) For linked lists, mergesort is the typical choice. While I was looking for a optimized implementation of mergesort for linked lists, I couldn't find one. I read something about Mcilroy's "Optimistic Merge Sort" and studied some implementation, but they were for...
5
1830
by: Chad | last post by:
I was looking at some old posts in comp.lang.c and found the following http://groups.google.com/group/comp.lang.c/browse_thread/thread/d26abbdf4d99abd9/b3b5046326994e18?hl=en&lnk=gst&q=recurrence+relation#b3b5046326994e18 I have some questions regarding the post. First, and I quote "Given an algorithm with loops or recursive calls, the...
0
7493
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language...
0
8008
jinu1996
by: jinu1996 | last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that...
0
7854
tracyyun
by: tracyyun | last post by:
Dear forum friends, With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the...
1
5411
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules. He will explain when you may want to use classes...
0
5133
by: conductexam | last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one. At the time of converting from word file to html my equations which are in the word document file was convert...
0
3525
by: adsilva | last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
1
1992
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
1
1107
muto222
by: muto222 | last post by:
How can i add a mobile payment intergratation into php mysql website.
0
808
bsmnconsultancy
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.