擅长:python、mysql、java
<p>标准<code>dict</code>:</p>
<pre><code>>>> dict2 = {}
>>> for key, values in dict1.items():
... for value in values:
... dict2.setdefault(value, []).append(key)
...
>>> dict2
{1: ['a', 'c', 'b'], 2: ['a', 'c', 'b'], 3: ['a', 'b'], 4: ['b']}
</code></pre>
<p><a href="http://docs.python.org/2/library/collections.html#collections.defaultdict" rel="nofollow">^{<cd2>}</a>:</p>
^{pr2}$