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Prefer mutative variant of delete for HashTable

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Instead of calling `filter(..)`.
This commit is contained in:
William Carroll 2020-11-16 17:13:39 +00:00
parent a457a81bbb
commit a2fa88f561
1 changed files with 16 additions and 3 deletions
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19
scratch/facebook/polynomial-rolling-hash.py
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@ -5,9 +5,12 @@ def compute_hash(x):
x[0] * P^0 + x[1] * P^1 + ... x[n-1] * P^(n-1) % M x[0] * P^0 + x[1] * P^1 + ... x[n-1] * P^(n-1) % M
P and M are constants. P and M are constants where P represents the next available prime number
that's GTE the number of unique characters you'll be hashing. In the case of
all lowercase characters, of which there are 26, the next available prime
number is 31.
""" """
p = 31 # small prime number p = 31
m = int(10e9) + 9 # large prime number m = int(10e9) + 9 # large prime number
power = 0 power = 0
result = 0 result = 0
@ -18,6 +21,9 @@ def compute_hash(x):
class HashTable(object): class HashTable(object):
def __init__(self, size): def __init__(self, size):
"""
Create a hash table with `size` buckets.
"""
buckets = [] buckets = []
for _ in range(size): for _ in range(size):
buckets.append([]) buckets.append([])
@ -55,5 +61,12 @@ class HashTable(object):
self.xs[h].append((key, val)) self.xs[h].append((key, val))
def delete(self, key): def delete(self, key):
"""
Remove entry `key` from the hash table.
"""
h = self.compute_hash(key) h = self.compute_hash(key)
self.xs[h] = list(filter(lambda entry: entry[0] != key, self.xs[h])) for i in range(len(self.xs[h])):
k, v = self.xs[h][i]
if k == key:
self.xs[h].remove((k, v))
return