City names game

p$*.permutation.find{|i|i*?,!~/(.),(?!\1)/i}

Yet another ruby implementation. Uses also case insensitive regex (as Ventero's old solution) but the test is done differently.

Previous version:

p$*.permutation.find{|i|(i*?,).gsub(/(.),\1/i,"")!~/,/}

Python (162 141 124)

Brute force for the win.

from itertools import*
print[j for j in permutations(raw_input().split())if all(x[-1]==y[0].lower()for x,y in zip(j,j[1:]))]

New solution is based on Howard's solution:

p$*.permutation.max_by{|i|(i*?,).scan(/(.),\1/i).size}

This uses the fact that there'll always be a valid solution.

Old solution, based on w0lf's solution:

p$*.permutation.find{|i|i.inject{|a,e|a&&e[0]=~/#{a[-1]}/i&&e}}