Find common characters

Time: O(NxL); Space: O(1); easy

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: A = [“bella”,“label”,“roller”]

Output: [“e”,“l”,“l”]

Example 1:

Input: A = [“cool”,“lock”,“cook”]

Output: [“c”,“o”]

Notes:

• 1 <= len(A) <= 100

• 1 <= len(A[i]) <= 100

• A[i][j] is a lowercase letter

import collections

class Solution1(object):
    def commonChars(self, A):
        """
        :type A: List[str]
        :rtype: List[str]
        """
        result = collections.Counter(A[0])
        for a in A:
            result &= collections.Counter(a)
        return list(result.elements())

s = Solution1()
A = ["bella", "label", "roller"]
assert s.commonChars(A) == ["e", "l", "l"]
A = ["cool", "lock", "cook"]
assert s.commonChars(A) == ["c", "o"]

See also:

https://leetcode.com/problems/find-common-characters