1002. Find Common Characters

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"]

Note:

1. 1 <= A.length <= 100
2. 1 <= A[i].length <= 100
3. A[i][j] is a lowercase letter

Approach #1: Array. [Java]

class Solution {
    public List<String> commonChars(String[] A) {
        List<String> ret = new ArrayList<>();
        int[] count = new int[26];
        Arrays.fill(count, Integer.MAX_VALUE);
        for (String a : A) {
            int[] cnt = new int[26];
            for (char c : a.toCharArray()) ++cnt[c-‘a‘];
            for (int i = 0; i < 26; ++i) count[i] = Math.min(count[i], cnt[i]);
        }
        for (int i = 0; i < 26; ++i) 
            while (count[i]-- > 0) 
                ret.add(""+(char)(i + ‘a‘));
        
        return ret;
    }
}

Reference:

https://leetcode.com/problems/find-common-characters/discuss/247558/Java-12-liner-count-and-look-for-minimum.