[LeetCode]#1002. Find Common Characters

Environment: Python 3.8

Key technique: Counter

Given an array A of strings made only from lowercase letters, return a list of all characters that show up in all strings within the list (including duplicates). For example, if a character occurs 3 times in all strings but not 4 times, you need to include that character three times in the final answer.

You may return the answer in any order.

Example 1:

Input: ["bella","label","roller"]
Output: ["e","l","l"]

Example 2:

Input: ["cool","lock","cook"]
Output: ["c","o"]

Analysis:

1. Use Counter for counting A[0] string.
2. Check c &= A[1] result
3. Check c &= A[2] result
4. Return result

Solution:

from collections import Counter
class Solution:
    def commonChars(self, A):
        if not A:
            return None
        
        c = Counter(A[0])            
        for word in A[1:]:
            c &= Counter(word)
                    
        ans = []
        for x in c:
            ans += [x] * c[x]
        return ans

Submissions:

Reference:

https://leetcode.com/problems/find-common-characters/discuss/1015608/clean-python-solution