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

vector<string> commonChars(vector<string>& A) { // time: O(n * m); space: O(m), where n is size of A array, m is the average length of string in the A array
    vector<int> cnt(26, INT_MAX);
    vector<string> res;
    for (string& s : A) {
        vector<int> cnt1(26, 0);
        for (char& c : s) ++cnt1[c - 'a'];
        for (int i = 0; i < 26; ++i) cnt[i] = min(cnt[i], cnt1[i]);
    }
    for (int i = 0; i < 26; ++i) {
        for (int j = 0; j < cnt[i]; ++j) {
            res.push_back(string(1, i + 'a'));
        } 
    }
    return res;
}