tvl-depot/users/wpcarro/scratch/facebook/polynomial-rolling-hash.py

def compute_hash(x):
    """
    Compute a unique fingerprint for the string input, `x`, as an integer using
    the following equation:

    x[0] * P^0 + x[1] * P^1 + ... x[n-1] * P^(n-1) % M

    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
    m = int(10e9) + 9 # large prime number
    power = 0
    result = 0
    for c in x:
        result += ord(c) * p**power
        power += 1
    return result % m

class HashTable(object):
    def __init__(self, size):
        """
        Create a hash table with `size` buckets.
        """
        buckets = []
        for _ in range(size):
            buckets.append([])
        self.xs = buckets
        self.compute_hash = lambda k: compute_hash(k) % size

    def __repr__(self):
        result = []
        for bucket in self.xs:
            for entry in bucket:
                result.append(entry)
        return "HashTable({})".format(",".join(str(x) for x in result))

    def get(self, key):
        """
        Attempt to retrieve value stored under `key`.
        """
        h = self.compute_hash(key)
        for k, v in self.xs[h]:
            if k == key:
                return v
        return None

    def put(self, key, val):
        """
        Set `key` to `val`; update value at `key` if it already exists.
        """
        h = self.compute_hash(key)
        for i in range(len(self.xs[h])):
            # Update entry if the key exists...
            if self.xs[h][i][0] == key:
                self.xs[h][i] = (key, val)
                return None
        # ...create a new entry otherwise
        self.xs[h].append((key, val))

    def delete(self, key):
        """
        Remove entry `key` from the hash table.
        """
        h = self.compute_hash(key)
        for i in range(len(self.xs[h])):
            k, v = self.xs[h][i]
            if k == key:
                self.xs[h].remove((k, v))
                return