Programming Praxis

One Response to “No Exercise Today”

1. Jussi Piitulainen said

   May 21, 2016 at 5:43 PM

   A take on that interleaved sorting exercise: a minimal way to see even and odd positions as collections of their own right, backed by the actual store that contains them both. (This is Python.)

   class See(object):
   
       def __init__(self, store, length, index):
           self.store = store
           self.length = length
           self.index = index
   
       def __setitem__(self, x, vs):
           '''handle self[:] = vs when lengths match'''
           for k, o in enumerate(vs):
               self.store[self.index(k)] = o
   
       def __iter__(self):
           for k in range(self.length):
               yield self.store[self.index(k)]
   
   def demonstrate(data):
       every = See(data, len(data), lambda k: k)
       even = See(data, -(-len(data) // 2), lambda k: 2 * k)
       odd = See(data, len(data) // 2, lambda k: 2 * k + 1)
       print('before:', *map(''.join, (every, even, odd)))
       even[:] = sorted(even)
       odd[:] = sorted(odd, reverse = True)
       print('after:', *map(''.join, (every, even, odd)))
   
   demonstrate(list('abracadabra'))
   demonstrate(list('0123456789'))
   
   # before: abracadabra arcdba baaar
   # after: arabbacadar aabcdr rbaaa
   # before: 0123456789 02468 13579
   # after: 0927456381 02468 97531