chain_hash_map.py

# Copyright 2013, Michael H. Goldwasser
#
# Developed for use with the book:
#
#    Data Structures and Algorithms in Python
#    Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
#    John Wiley & Sons, 2013
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

from hash_map_base import HashMapBase
from unsorted_table_map import UnsortedTableMap

class ChainHashMap(HashMapBase):
  """Hash map implemented with separate chaining for collision resolution."""

  def _bucket_getitem(self, j, k):
    bucket = self._table[j]
    if bucket is None:
      raise KeyError('Key Error: ' + repr(k))        # no match found
    return bucket[k]                                 # may raise KeyError

  def _bucket_setitem(self, j, k, v):
    if self._table[j] is None:
      self._table[j] = UnsortedTableMap()     # bucket is new to the table
    oldsize = len(self._table[j])
    self._table[j][k] = v
    if len(self._table[j]) > oldsize:         # key was new to the table
      self._n += 1                            # increase overall map size

  def _bucket_delitem(self, j, k):
    bucket = self._table[j]
    if bucket is None:
      raise KeyError('Key Error: ' + repr(k))        # no match found
    del bucket[k]                                    # may raise KeyError

  def __iter__(self):
    for bucket in self._table:
      if bucket is not None:                         # a nonempty slot
        for key in bucket:
          yield key