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Mark Pilgrim
2009-08-05 14:49:32 -07:00
parent 202511e983
commit fb0aa874df
17 changed files with 231 additions and 197 deletions
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@@ -45,7 +45,7 @@ E = 4</code></pre>
<p>In this chapter, we&#8217;ll dive into an incredible Python program originally written by Raymond Hettinger. This program solves alphametic puzzles <em>in just 14 lines of code</em>.
<p class=d>[<a href=examples/alphametics.py>download <code>alphametics.py</code></a>]
<pre><code class=pp>import re
<pre class=pp><code>import re
import itertools
def solve(puzzle):
@@ -150,7 +150,7 @@ if __name__ == '__main__':
<p>The alphametics solver uses this technique to get a list of all the unique characters in the puzzle.
<pre class=nd><code class=pp>unique_characters = set(''.join(words))</code></pre>
<pre class='nd pp'><code>unique_characters = set(''.join(words))</code></pre>
<p>This list is later used to assign digits to characters as the solver iterates through the possible solutions.
@@ -178,11 +178,11 @@ AssertionError: Only for very large values of 2</samp></pre>
<p>Therefore, this line of code:
<pre class=nd><code class=pp>assert len(unique_characters) <= 10, 'Too many letters'</code></pre>
<pre class='nd pp'><code>assert len(unique_characters) <= 10, 'Too many letters'</code></pre>
<p>&hellip;is equivalent to this:
<pre class=nd><code class=pp>if len(unique_characters) > 10:
<pre class='nd pp'><code>if len(unique_characters) > 10:
raise AssertionError('Too many letters')</code></pre>
<p>The alphametics solver uses this exact <code>assert</code> statement to bail out early if the puzzle contains more than ten unique letters. Since each letter is assigned a unique digit, and there are only ten digits, a puzzle with more than ten unique letters can not possibly have a solution.
@@ -217,7 +217,7 @@ AssertionError: Only for very large values of 2</samp></pre>
<p>Here&#8217;s another way to accomplish the same thing, using a <a href=generators.html>generator function</a>:
<pre class=nd><code class=pp>def ord_map(a_string):
<pre class='nd pp'><code>def ord_map(a_string):
for c in a_string:
yield ord(c)
@@ -413,7 +413,7 @@ Wesley</samp></pre>
<p id=guess>The alphametics solver uses this technique to create a dictionary that maps letters in the puzzle to digits in the solution, for each possible solution.
<pre class=nd><code class=pp>characters = tuple(ord(c) for c in sorted_characters)
<pre class='nd pp'><code>characters = tuple(ord(c) for c in sorted_characters)
digits = tuple(ord(c) for c in '0123456789')
...
for guess in itertools.permutations(digits, len(characters)):