A Python solution to the "How to Lose an IT Job in 10 Minutes" puzzle

city_names.py

#!/usr/bin/env python
# From https://hackernoon.com/how-to-lose-an-it-job-in-10-minutes-3d63213c8370
#
# Find cities whose names are rotated versions of other cities.
#
# Given: ['Tokyo', 'London', 'Rome', 'Donlon', 'Kyoto', 'Paris']
#
# Return:
#
#[[ 'Tokyo', 'Kyoto' ],
# [ 'London', 'Donlon' ],
# [ 'Rome' ],
# [ 'Paris' ]]
import collections

__author__ = "David Blume"
__license__ = "MIT"


def find_matches(cities):
    d = collections.defaultdict(list)
    for city in cities:
        lc = city.lower()
        # Easy for me to understand, but room for speed optimizations
        k = sorted([lc[i:]+lc[:i] for i in range(len(lc))])[0]
        d[k].append(city)
    return d.values()

print find_matches(("Tokyo", "London", "Rome", "Donlon", "Kyoto", "Paris"))