擅长:python、mysql、java
<pre><code>d = {
'A': ['Blue'],
'B': ['A'],
'C': ['A'],
'D': ['C'],
}
output = {}
for k, v in d.items():
output[v[0]] = output.get(v[0], [])
output[v[0]].append(k)
output
#=> {'Blue': ['A'], 'A': ['C', 'B'], 'C': ['D']}
</code></pre>