/in/foo.cc: In member function 'void Solution::function()':
/in/foo.cc:32:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (front = 0; front < input.length(); front++)
                   ~~~~~~^~~~~~~~~~~~~~~~
/in/foo.cc:43:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (rear = front; rear < input.length(); rear++)
                       ~~~~~^~~~~~~~~~~~~~~~