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POPython: adding 1 print Kills my code?
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copied!<p>I was playing with this sudoku solver, that I found.</p> <p>Like quoted here it works perfect, but if I uncomment that single <code>print a</code>, that I commented out (line 13), then it stops before finding a full solution...?</p> <pre><code>import sys from datetime import datetime # for datetime.now() def same_row(i,j): return (i/9 == j/9) def same_col(i,j): return (i-j) % 9 == 0 def same_block(i,j): return (i/27 == j/27 and i%9/3 == j%9/3) def r(a): i = a.find('.') if i == -1: # All solved ! print a else: #print a excluded_numbers = set() for j in range(81): if same_row(i,j) or same_col(i,j) or same_block(i,j): excluded_numbers.add(a[j]) for m in '123456789': if m not in excluded_numbers: # At this point, m is not excluded by any row, column, or block, so let's place it and recurse r(a[:i]+m+a[i+1:]) if __name__ == '__main__': if len(sys.argv) == 2: filI = open(sys.argv[1]) for pusI in filI: pusI.strip() print "pussle:\n",pusI timStart = datetime.now() r(pusI) # <- Calling the recursive solver ... timEnd = datetime.now() print "Duration (h:mm:ss.dddddd): "+str(timEnd-timStart) else: print str(len(sys.argv)) print 'Usage: python sudoku.py puzzle' </code></pre> <p>The program needs to be called with a file. That file should hold 1 sudoku per line.</p> <p>For testing I used this:</p> <pre><code>25...1........8.6...3...4.1..48.6.9...9.4.8...1..29.4.9.53.7....6..5...7......... </code></pre> <p><strong>QUESTION:</strong></p> <p>I can't understand how that single 'print a' manage to break the recursive loop, before it's done. Can anyone give an explanation?</p> <p>Best regards Martin@Hvidberg.net</p> <p>Credit: I originally found the above sudoku solver code here: <a href="http://www.scottkirkwood.com/2006/07/shortest-sudoku-solver-in-python.html" rel="nofollow noreferrer">http://www.scottkirkwood.com/2006/07/shortest-sudoku-solver-in-python.html</a> it's also shown here on StackOverflow: <a href="https://stackoverflow.com/questions/201461/shortest-sudoku-solver-in-python-how-does-it-work">Shortest Sudoku Solver in Python - How does it work?</a></p>

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