import string
import random
import hashlib

letters = string.ascii_lowercase + string.ascii_uppercase

# 4a

def H(m: str) -> str:
    return hashlib.sha256(m.encode()).hexdigest()[:2]


counts = []
for n in range(20):
    i = 0
    hashes = []
    messages = []
    while True:

        n_char = random.randint(1, 1000)
        m = ''.join([random.choice(letters) for n in range(n_char)])
        hm = H(m)

        # print(i)
        # print(m)
        # print(hm)

        if hm in hashes:
            counts.append(i)
            break
        else:
            hashes.append(hm)
            messages.append(m)

        i += 1

print(f'Average number of trials for a collision: {sum(counts)/len(counts)}')