Most Common Word Python Solution with Tests

lcpy gen -n 819   # by problem number
lcpy gen -s most_common_word   # by problem name

Input: paragraph = "Bob hit a ball, the hit BALL flew far after it was hit.", banned = ["hit"]
Output: "ball"
Explanation: "hit" occurs 3 times, but it is a banned word. "ball" occurs twice (and no other word does), so it is the most frequent non-banned word in the paragraph.

Input: paragraph = "a.", banned = []
Output: "a"

import re


class Solution:
    # Time: O(P + B)
    # Space: O(P)
    def most_common_word(self, paragraph: str, banned: list[str]) -> str:
        banned_set = set(banned)
        counts: dict[str, int] = {}
        for word in re.findall(r"[a-z]+", paragraph.lower()):
            if word not in banned_set:
                counts[word] = counts.get(word, 0) + 1
        return max(counts, key=lambda w: counts[w])