Why do we add 1 to the r + m in the last line ?

Question

0.00/5 (No votes)

See more:

Python

def bsearch ( lst : list , key ):
    n = len ( lst )
    if n == 0:
        return None # key not in empty list
    m = n //2 # position of root
    if lst [ m ] == key :
        return m
    elif lst [ m ] > key :
        return bsearch ( lst [: m ] , key )
    else : # lst[m] < key
        r = bsearch ( lst [ m +1:] , key )
        return None if r is None else r + m +1

What I have tried:

.........................................mnm..

Posted 11-Sep-20 14:43pm

Ahmad Qassym

Updated 11-Sep-20 16:21pm

Add a Solution

Comments

Richard MacCutchan 12-Sep-20 3:24am

Ask the person who wrote the code.

Ahmad Qassym 12-Sep-20 9:01am

:)

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Patrice T · Answer 1 · 2020-09-11T16:22:00

Quote:
Why do we add 1 to the r + m in the last line ?

Use the debugger and see when and why this line of code is executed.
May be both m+1 are linked:

Python

r = bsearch ( lst [ m +1:] , key )
return None if r is None else r + m +1

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

27.3. pdb — The Python Debugger — Python 3.6.1 documentation[^]
Debugging in Python | Python Conquers The Universe[^]
pdb – Interactive Debugger - Python Module of the Week[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Why do we add 1 to the r + m in the last line ?

1 solution

Solution 1

Add your solution here

Preview 0

Existing Members

...or Join us