819. Most Common Word

Description

Given a string paragraph and a string array of the banned words banned, return the most frequent word that is not banned. It is guaranteed there is at least one word that is not banned, and that the answer is unique.

The words in paragraph are case-insensitive and the answer should be returned in lowercase.

info

You can read the full description here.

Solution

Approach

1. Delete other characters except for alnum+underscore with re.sub.
2. List Comprehension makes code simple.

Implementation

import collections
import re
from typing import List

class Solution:
    def mostCommonWord(self, paragraph: str, banned: List[str]) -> str:
        words = [word for word in re.sub(r'[^\w]', ' ', paragraph)
            .lower().split()
                 if word not in banned]

        counts = collections.Counter(words)

        # print(counts.most_common(1)) -> [('ball',2)]
        return counts.most_common(1)[0][0]

Complexity Analysis

• $n$: length of paragraph, $m$: length of banned
• Time Complexity: $O(nm)$
• Space Complexity: $O(n)$