Path: csiph.com!usenet.pasdenom.info!news.albasani.net!newsfeed.freenet.ag!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'python.': 0.02; 'suppose': 0.07; '"r"': 0.09; 'explanation': 0.09; 'friday,': 0.09; 'function,': 0.09; 'parameter': 0.09; 'returns,': 0.09; 'specified,': 0.09; 'term,': 0.09; 'to:addr:comp.lang.python': 0.09; 'val': 0.09; 'way:': 0.09; 'windows,': 0.09; 'translate': 0.10; 'cc:addr:python-list': 0.11; 'python': 0.11; 'def': 0.12; 'command.': 0.16; 'definition.': 0.16; 'integer,': 0.16; 'integer.': 0.16; 'loop.': 0.16; 'nonzero': 0.16; 'zero,': 0.16; 'applies': 0.16; 'thursday,': 0.16; 'wrote:': 0.18; 'code.': 0.18; 'all,': 0.19; 'meant': 0.20; 'solution.': 0.20; 'command': 0.22; 'code,': 0.22; 'programming': 0.22; 'cc:addr:python.org': 0.22; 'header:User-Agent:1': 0.23; 'integer': 0.24; 'specify': 0.24; 'cc:2**0': 0.24; 'cc:no real name:2**0': 0.24; "i've": 0.25; 'switch': 0.26; 'defined': 0.27; 'header:In-Reply-To:1': 0.27; 'function': 0.29; 'bigger': 0.30; 'matching': 0.30; 'closer': 0.31; 'implied': 0.31; 'linux.': 0.31; 'stands': 0.31; 'another': 0.32; 'definition': 0.35; 'no,': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'building': 0.35; 'doing': 0.36; 'next': 0.36; 'example,': 0.37; 'so,': 0.37; 'level': 0.37; 'thank': 0.38; 'needed': 0.38; 'files': 0.38; 'pm,': 0.38; 'explain': 0.39; 'does': 0.39; 'itself': 0.39; 'dave': 0.60; 'march': 0.61; 'skip:* 10': 0.61; "you're": 0.61; 'further': 0.61; 'first': 0.61; 'back': 0.62; "you'll": 0.62; 'skip:n 10': 0.64; 'more': 0.64; 'levels': 0.65; 'receive': 0.70; 'anyone.': 0.74; 'discover': 0.82; 'vba': 0.84; 'angel': 0.91; '2013': 0.98 X-Received: by 10.50.217.225 with SMTP id pb1mr2376506igc.5.1364533647508; Thu, 28 Mar 2013 22:07:27 -0700 (PDT) Newsgroups: comp.lang.python Date: Thu, 28 Mar 2013 22:07:27 -0700 (PDT) In-Reply-To: Complaints-To: groups-abuse@google.com Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=122.151.65.43; posting-account=JzVE4wkAAADCSo8EXJLK0dGqAu47aMvq References: <9dla2a-kql.ln1@satorlaser.homedns.org> <5ce10a13-be58-4548-85df-e1d865d3304e@googlegroups.com>

User-Agent: G2/1.0 X-Google-Web-Client: true X-Google-IP: 122.151.65.43 MIME-Version: 1.0 Subject: Re: Sudoku From: Eric Parry To: comp.lang.python@googlegroups.com Content-Type: text/plain; charset=ISO-8859-1 Cc: python-list@python.org X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Message-ID: Lines: 131 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1364535726 news.xs4all.nl 6847 [2001:888:2000:d::a6]:57315 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:42225 On Friday, March 29, 2013 9:58:27 AM UTC+10:30, Dave Angel wrote: > On 03/28/2013 06:11 PM, Eric Parry wrote: > > > On Thursday, March 28, 2013 3:06:02 PM UTC+10:30, Dave Angel wrote: > > > > > > > > >> > > >> > > >> Are you familiar with recursion? Notice the last line in the function > > >> r() calls the function r() inside a for loop. > > >> > > >> So when r() returns, you're back inside the next level up of the > > >> function, and doing a "backtrack." > > >> > > >> When the function succeeds, it will be many levels of recursion deep. > > >> For example, if the original pattern had 30 nonzero items in it, or 51 > > >> zeroes, you'll be 51 levels of recursion when you discover a solution. > > >> > > >> If you don't already understand recursion at all, then say so, and one > > >> or more of us will try to explain it in more depth. > > >> > > > > > > > > Thank you for that explanation. > > > No, I do not understand recursion. It is missing from my Python manual. I would be pleased to receive further explanation from anyone. > > > Eric. > > > > > > > Recursion is not limited to Python. It's a general programming term, > > and indeed applies in other situations as well. Suppose you wanted to > > explain what the -r switch meant in the cp command. "r" stands for > > recursion. > > > > (example is from Linux. But if you're more familiar with Windows, it's > > the /s switch in the DIR command.) > > > > The cp command copies all the matching files in one directory to another > > one. If the -r switch is specified, it then does the same thing to each > > subdirectory. > > > > Notice we did NOT have to specify sub-subdirectories, since they're > > recursively implied by the first description. > > > > > > Closer to the current problem, suppose you defined factorial in the > > following way: factorial(0) is 1, by definition. And for all n>0, > > factorial(n) is n*factorial(n-1). > > > > So to directly translate this definition to code, you write a function > > factorial() which takes an integer and returns an integer. If the > > parameter is zero, return one. If the parameter is bigger than zero, > > then the function calls itself with a smaller integer, building up the > > answer as needed (untested). > > > > def factorial(n): > > if n==0: > > return 1 > > val = n *factorial(n-1) > > return val > > > > > > > > > > -- > > DaveA Thank you for that Dave, I've started writing the VBA code. Eric.