Created
April 10, 2014 01:26
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INIT_SIZE = 10 | |
MAX_AVG_COLLISIONS = 1 | |
FREQ_OF_COLLISIONS_CHECK = 0.67 | |
class HashTable(object): | |
def __init__(self): | |
self.arr = self._create_array(INIT_SIZE) | |
self.insert_counter = 0 | |
def _create_array(self, size): | |
return [[] for x in range(size)] | |
def __len__(self): | |
return len([x for x in self.arr if x is not None]) | |
def insert(self, key, value): | |
hashed_index = self._hash_index(key) | |
self.arr[hashed_index].append((key,value)) | |
self._handle_collisions() | |
def lookup(self, key): | |
hashed_index = self._hash_index(key) | |
collision_index = self._sequential_search(self.arr[hashed_index], key) | |
return self.arr[hashed_index][collision_index][1] | |
def delete(self, key): | |
hashed_index = self._hash_index(key) | |
try: | |
collision_index = self._sequential_search(self.arr[hashed_index], key) | |
del self.arr[hashed_index][collision_index] | |
except KeyError: | |
pass | |
def _handle_collisions(self): | |
self.insert_counter += 1 | |
if self.insert_counter > len(self.arr): | |
if self._avg_collision_length() > MAX_AVG_COLLISIONS: | |
self._resize() | |
def _avg_collision_length(self): | |
return sum([len(x) for x in self.arr])/len(self.arr) | |
def _resize(self): | |
print "Avg # of collision before resize: " + str(self._avg_collision_length()) | |
new_arr = self._create_array(len(self.arr)*2) | |
tmp_arr = self.arr | |
self.arr = new_arr | |
for collision_array in tmp_arr: | |
for item in collision_array: | |
self.insert(*item) | |
self.insert_counter = 0 | |
print "Avg # of collision after resize: " + str(self._avg_collision_length()) | |
def _sequential_search(self, collisions, key): | |
for i, x in enumerate(collisions): | |
if x[0] == key: | |
return i | |
else: | |
raise KeyError("Item not found") | |
def _hash_index(self, key): | |
hashed_key = current_hash(key) | |
hashed_index = hashed_key % len(self.arr) | |
return hashed_index | |
def test(): | |
x = HashTable() | |
x.insert('foo','hi') | |
print x.lookup('foo') == 'hi' | |
x.insert('ofo','1') | |
print x.lookup('foo') == 'hi' | |
print x.lookup('ofo') == '1' | |
x.delete('ofo') | |
try: | |
x.lookup('ofo') | |
except KeyError: | |
print 'delete succeeded' | |
print x.delete('ofo') == None | |
print x.lookup('foo') == 'hi' | |
def test2(): | |
x = HashTable() | |
x.insert('fooamskdlfalfkmds','foo') | |
x.insert('ofoasdddddddddddddfffff','ofo') | |
x.insert('oofcccccccccccccccc','oof') | |
x.insert('dddddddddddddd','bar') | |
x.insert('eeeeeeeeeeee','baz') | |
x.insert('fffffffffffffffffff','non') | |
x.insert('ggggggggggggggggggg','xyz') | |
x.insert('fooamskylfalfkmys','foo') | |
x.insert('ofoasyyyyyyyyyyyyyfffff','ofo') | |
x.insert('oofqqqqqqqqqqqqqqqq','oof') | |
x.insert('yyyyyyyyyyyyyy','ear') | |
x.insert('eeeadsfdsfeeeeeeeee','eaz') | |
x.insert('fffsadfadsfffffffffffffffff','non') | |
x.insert('aaaaaaaaaaaaaaaaaaa','xyz') | |
x.insert('fooamskdlfmmds','foo') | |
x.insert('ofdddddddfffff','ofo') | |
x.insert('oofcccccccqqqqccccccc','oof') | |
x.insert('ddddccccccddddd','bar') | |
x.insert('eeeewweeeeee','baz') | |
x.insert('ffffffeeeeeeeewefffffffff','non') | |
x.insert('gggggwwwwwgggwgggggg','xyz') | |
x.insert('ddddccccccddwddad','bar') | |
x.insert('eeeewweeeeawaaee','baz') | |
x.insert('ffffffeeeeweeeeaaaaefffffffff','non') | |
x.insert('gggggwwwwwgggggggsaaaagg','xyz') | |
x.insert('fooamskylfalfkmyss','foo') | |
x.insert('ofoasyyyyyyyyyysyyyfffff','ofo') | |
x.insert('oofqqqqqqqqqqqsqqqqq','oof') | |
x.insert('yyyyyyyyyyyyysy','ear') | |
x.insert('eeeadsfdsfeeeeseeeee','eaz') | |
x.insert('fffsadfadsfffsffffffffffffff','non') | |
x.insert('aaaaaaaaaaaasaaaaaaa','xyz') | |
x.insert('fooamskdlfmsmds','foo') | |
x.insert('ofdddddddfsffff','ofo') | |
x.insert('oofccccccscqqqqccccccc','oof') | |
x.insert('ddddccccccdsdddd','bar') | |
x.insert('eeeewweeeesee','baz') | |
x.insert('ffffffeeeeeeeseefffffffff','non') | |
x.insert('gggggwwwwwgggsgggggg','xyz') | |
x.insert('ddddccccccddsddad','bar') | |
x.insert('eeeewweeeeaasaee','baz') | |
x.insert('ffffffeeeeeeeeaaaaesfffffffff','non') | |
x.insert('gggggwwwwwgggggggaasaagg','xyz') | |
def current_hash(s): | |
return my_djb2(s) | |
def dumb_hash(s): | |
return sum([ord(p) for p in s]) | |
def my_djb2(s): | |
result = 5381 | |
for c in s: | |
result = ((result << 5) + result) + ord(c) | |
return result | |
if __name__ == '__main__': | |
test2() |
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